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Outsourced Accounting Services for UK Businesses at a Fraction of an In-House Hire

Bookkeeping | VAT & Self-Assessment | Company Formation | Payroll | CFO Advisory 

Running a UK business means answering to HMRC and Companies House, on different clocks, with different penalties. Our outsourced accounting services keep your books, VAT and Corporation Tax filed on time, MTD-ready, checked by AI first and a qualified accountant always, the kind of online accounting services that take deadlines off your plate entirely. 

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About

The Maths Behind Building a Finance Team In-House

Hiring a Finance Director for a growing UK business costs £90,000 to £150,000 a year in base salary alone. Add a senior accountant on up to £80,000, then a payroll specialist and a bookkeeper on top, and the costs stack fast, before National Insurance, pension contributions, and recruitment fees, which typically run 20 to 30 percent of first-year salary before anyone’s even started. For most growing businesses, that math doesn’t work. 

So, we built Maspartner to close that gap. 

You get ACA, ACCA and credentialed professionals across every discipline, working inside the software you already use: Xero, QuickBooks, Sage, and more. Every project is backed by the same standard we bring to small business bookkeeping services as we do to full-scale outsourced accounting services for growing companies. 

Over 250+ businesses across the UK run their finances through us.  We handle the full financial picture, at a fraction of the cost of building it in-house. 

Making Tax Digital Handled From Day One

We check your MTD status the moment you come on board, set up HMRC-recognised software, and handle your quarterly updates and Final Declaration so nothing slips through. No letter from HMRC required to find out where you stand, we tell you first. 

Is your business affected? The MTD for income tax 2026 - 2028 roadmap

Deadline Income Status
6th April 2026 Over £50,000 Filing deadline passed Take action today!
6th April 2027 Over £30,000 Plan and prepare now Take action today!
6th April 2028 Over £20,000 Future compliance Take action today!
services

AI-Powered Outsourced Accounting Services in One Place

Our accounting and bookkeeping services are built around automated financial management and a team of qualified UK accountants who understand what HMRC and Companies House expect. From AI-driven checks that flag issues before they reach a filing, to Finance Director (FD) advisory that helps you plan, pick the services built for where your business is today.

Bookkeeping

Transaction categorisation, bank reconciliation, ledger maintenance

Self Assessment (SA100)

Income and expense schedules, allowable expense claims, tax computation and filing 

VAT Registration & Returns

VAT registration, output and input VAT calculation, quarterly return submission 

Making Tax Digital Set-Up

Digital record-keeping, MTD-compatible software configuration, quarterly update submission 

Payroll Management

PAYE registration, RTI submissions (FPS/EPS), payslip generation 

Trademark Registration

Clearance search, Nice Classification, IPO filing 

Company Formation & Business Set-Up

Companies House incorporation, Memorandum and Articles of Association, SIC code classification 

Bookkeeping & Financial Statements

Double-entry bookkeeping, trial balance preparation, financial statement drafting 

Credit Control

Aged debtor reporting, invoice chasing, payment terms enforcement 

Management Accounts

P&L and balance sheet reporting, variance analysis, KPI tracking 

Corporation Tax & Companies House Filings

CT600 computation, capital allowances, annual accounts and confirmation statement filing 

R&D Tax Credit Support

Qualifying expenditure identification, R&D claim preparation, HMRC submission

Payroll Management

PAYE registration, RTI submissions (FPS/EPS), P11D and benefits-in-kind reporting 

Trademark Registration

Clearance search, Nice Classification, IPO filing and opposition monitoring 

CFO & Advisory Services

Cash flow forecasting, budget variance analysis, financial modelling 

White-Label Bookkeeping

Ledger maintenance and reconciliation delivered under your firm’s branding 

Historical Books Cleanup

backlog reconciliation, prior-period adjustments, opening balance corrections 

VAT Return Preparation

VAT workpaper preparation, return computation, client-ready review packs 

Payroll Processing for Multiple Clients

Multi-client RTI submissions, payslip batching, PAYE reconciliation 

Overflow Tax Preparation

SA100 and CT600 preparation for peak-season capacity support 

Audit Support

Working paper preparation, sample testing support, reconciliation schedules 

Why Clients Choose maspartner?

Beyond offering services, we complement your journey with our commitment to Satisfaction.

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Experience is the key to knowledge.

At Mercurius Advisory Services, we’ve cultivated a culture that values expertise, genuine care, and lasting partnerships. Our services are designed to provide you with unparalleled support, offering solutions built on years of experience. Explore our comprehensive offerings to empower your business.

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Interested in our services or want to inquire more? Just drop your email, and we’ll reach out to you.



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    The Expertise Behind Your Books

    Most accounting problems aren’t accounting problems. They’re visibility problems, and in the UK, they’re compliance problems too. 

    Co-founders Siddhartha Havelia and Ankit Jain spent years inside global advisory practices watching growing businesses lose track of their numbers the moment reporting got complex. That’s what shaped Maspartner UK: a practice built so your books stay accurate, your filings stay on time, and your compliance never depends on you remembering a deadline. 

    It’s the same standard behind every one of our online accounting services, whether it’s a single VAT return or full year-round bookkeeping. 

    Every client’s data is handled under UK GDPR, with strict verification and confidentiality checks built into how we onboard and manage every engagement before we ever touch your financial data. 

    Planning to Set Up in the EU Next? We Handle That Too.

    Already trading in the UK and thinking about a European entity? We support businesses moving or expanding into the EU, from entity structuring to cross-border compliance, so growth doesn’t stall at the Channel. 

    DATA SECURITY

    Your Financial Data Is Protected to UK Standards

    We handle your financial information under UK GDPR, with strict confidentiality and security controls backed by clear data handling agreements on every engagement.

    Security Standards

    • GDPR Compliant 
    • ISO 27001 certified information security 
    • ISO 9001:2015 certified quality management 
    • Legally binding Non-Disclosure Agreements on every engagement 
    • Encrypted file transfer and storage 
    • Role-based, controlled employee access 
    • Strict data retention and disposal policy 

    Our Client Reviews

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    Suvir Salins profile picture
    Suvir Salins
    Google star 1Google star 2Google star 3Google star 4Google star 5Trustindex verifies that the original source of the review is Google.
    MAS provides a great service at an affordable price. Very timely and professional communication. Fast and accurate book keeping and tax services. Highly recommended.
    Posted on Google Google
    Abhishek profile picture
    Abhishek
    Google star 1Google star 2Google star 3Google star 4Google star 5Trustindex verifies that the original source of the review is Google.
    Highly recommended. Worked with Arun, he is very professional and swift in his work. Good experience with ITR filing.
    Posted on Google Google
    Richard Sherman profile picture
    Richard Sherman
    Google star 1Google star 2Google star 3Google star 4Google star 5Trustindex verifies that the original source of the review is Google.
    We have used Mercurius Advisory Services (MAS) for about 6 years now. They handle all of our bookkeeping for multiple companies and we have been VERY happy with them! Wonderful team and great work at a very fair price!
    Posted on Google Google
    Paul Scribner profile picture
    Paul Scribner
    Google star 1Google star 2Google star 3Google star 4Google star 5Trustindex verifies that the original source of the review is Google.
    I have worked with MAS LLP, and with Ankit and Siddhartha in particular, for over 10 years. Throughout that time they have been a consistently reliable and trusted partner. On the day to day side, Nilesh has been excellent to work with, and Yitesh has also been a pleasure to deal with. I am glad to recommend MAS to anyone looking for a dependable, professional team.
    Posted on Google Google
    Phillip Williamson profile picture
    Phillip Williamson
    Google star 1Google star 2Google star 3Google star 4Google star 5Trustindex verifies that the original source of the review is Google.
    Mercury does the bookkeeping and tax returns for my company. They do a great job at a reasonable price. They are attentive and very responsive. I really appreciate that they update my QuickBooks weekly and month-end reconciliations are done a day or two after month-end.
    Posted on Google Google
    Mark Switzer profile picture
    Mark Switzer
    Google star 1Google star 2Google star 3Google star 4Google star 5Trustindex verifies that the original source of the review is Google.
    A professional, complete range of services, with excellent execution.
    Posted on Google Google
    Gurbir Sidhu profile picture
    Gurbir Sidhu
    Google star 1Google star 2Google star 3Google star 4Google star 5Trustindex verifies that the original source of the review is Google.
    Great service. Have been with them for few years and always deliver on time and very easy to work with. Ankit and Sumit have been really awesome.
    Posted on Google Google
    Alejandro Colindres F. profile picture
    Alejandro Colindres F.
    Google star 1Google star 2Google star 3Google star 4Google star 5Trustindex verifies that the original source of the review is Google.
    Very smooth experience with Mercurius doing my quarterly books for my Amazon business. Always answered my questions and communication was seamless. Highly recommend!
    Posted on Google Google
    Kareena Black profile picture
    Kareena Black
    Google star 1Google star 2Google star 3Google star 4Google star 5Trustindex verifies that the original source of the review is Google.
    We’ve been using MAS for a few years to support our US bookkeeping and payroll, and they’ve been a highly reliable partner throughout. Their understanding of US compliance and operational requirements gives us a lot of confidence that everything is being handled properly behind the scenes. They’re responsive, communicative, and proactive in flagging anything that needs attention. As we’ve scaled, they’ve adapted well and continued to deliver a smooth, low friction experience. We’d happily recommend them to other teams operating in the US.

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    FAQs

    Outsourced accounting services means having an external provider manage functions such as bookkeeping, tax filings, payroll, and financial reporting instead of handling them entirely in-house. Maspartner’s outsourced accounting services cover everything from day-to-day bookkeeping to VAT, Corporation Tax, and Self Assessment, using the accounting software your business already works with. 

    An outsourced bookkeeper records and reconciles transactions, manages accounts payable and receivable, and keeps your books up to date each month. These records then give your accountant the accurate financial information needed for tax filings and reporting. Bookkeeping focuses on maintaining the records, while accounting uses those records for compliance, reporting, and financial planning. 

    Start by checking the provider’s qualifications, AML registration, services, and pricing. You can then connect your existing accounting software and transfer the necessary records. A good outsourced accounting services provider should also give you a clear point of contact and a straightforward handover process. At Maspartner, we can work with your existing accountant during the transition and request professional clearance where required, helping ensure important records are carried across properly. 

    Bookkeeping involves recording, categorising, and reconciling your day-to-day transactions. Outsourced accounting covers a wider range of work, including VAT returns, Corporation Tax filings, Self Assessment, financial statements, and financial reporting. Most businesses need both, which is why online accounting services can bring these functions together rather than managing them separately. 

    For many growing businesses, outsourced accounting services can be a practical alternative to hiring a full-time finance team. You can access qualified accounting support without taking on the full cost of salaries, recruitment, training, and staff cover. Very early-stage sole traders with few transactions may only need basic bookkeeping at first, while businesses with more complex finances may benefit from broader accounting support. 

    Yes. For Making Tax Digital for Income Tax, the relevant threshold is based on qualifying income rather than the profit left after expenses. This means a landlord with £55,000 of qualifying property income could fall within the rules even if their taxable profit is much lower. Maspartner can review your income and circumstances to help determine whether the MTD rules apply to you. 

    Yes. Your bookkeeper or accountant does not need to be based in your local area to manage your accounts. What matters is that your records are maintained properly, the relevant compliance requirements are met, and your tax returns and filings are prepared and reviewed correctly. Maspartner supports UK businesses remotely, so your location does not prevent you from using online accounting services. 

    Yes, professional accounting practices can outsource bookkeeping and other work, provided they meet their professional, confidentiality, data protection, and AML responsibilities. The practice remains responsible for choosing suitable providers and putting the appropriate agreements and controls in place. Maspartner also provides white-label accounting support for practices that need additional bookkeeping capacity without adding to their internal team. 

    It can be, particularly for small and growing businesses that do not need a full-time bookkeeper. An in-house employee can involve salary, employer National Insurance, pension contributions, recruitment, training, software, and holiday or sick cover. Small business bookkeeping services provide an alternative where you pay for the level of support your business needs, often through a fixed monthly fee. The right option depends on your transaction volume, accounting needs, and how much financial support you require. 

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