Switching accountants can be positive, but if the handover is messy, it can also trigger missed deadlines, gaps in records, and confusing letters from HMRC. When you hire an accountant in London, the change itself should not put your tax year at risk, yet it often does when timing, paperwork, and authorisations are not planned.
Many owners and landlords use late summer to review their finances. Year-end accounts may be done, the next tax season is coming, and you can see where you did not get the support you needed. If you are growing, own rental property, or you are a female founder who needs more proactive help, changing firm can unlock better advice and better systems. The key is to manage the switch with care so nothing falls between the two advisers.
Why an Accountant Switch Can Disrupt Your Tax Year
August is a natural pause for many London businesses. People return from holidays, cash flow is clearer after the first half of the year, and the next wave of VAT, PAYE, and Self Assessment deadlines is on the horizon. It is a common moment to ask whether your current accountant still fits your plans.
A new adviser can bring:
- Stronger tax planning as profits or rental income grow
- Better use of cloud software so you are not trapped in spreadsheets
- More tailored support, including for female entrepreneurs who need clear, practical guidance
The risk is that a rushed handover can cause:
- HMRC still speaking only to your old agent
- VAT or PAYE filings being assumed by each firm, then missed by both
- Records not arriving in time for the next Corporation Tax or Self Assessment filing
As an ICAEW regulated firm of chartered accountants in London, we see how often these issues appear only after a switch has already started.
Handover Gaps That Leave Your Business Exposed
A good handover is more than sending a backup of your accounts. Your new accountant needs a full picture so they can stand behind both old figures and new ones.
At a minimum, the outgoing accountant should provide:
- Year-end working papers and trial balances
- Management accounts and bank reconciliations
- Tax computations for the business and owners
- Fixed asset registers and depreciation schedules
- VAT workings for recent quarters
- Payroll records, RTI submissions, and P60s or P45s
- Copies of Companies House filings and confirmation statements
The hidden gaps often sit in the detail. For example,:
- Adjustments with no explanation, such as big journal entries at year end
- Missing support for key balances, like director loans or VAT control accounts
- Part-done reconciliations that were never fully cleared
Your new firm has to decide how much they can rely on past numbers. They may need time to review prior years before filing new returns or giving planning advice. If you hire an accountant in London halfway through a VAT quarter or close to company year-end, that review work can affect when they are comfortable filing.
Managing HMRC Authorisations Without Disruption
HMRC agent authorisation lets your accountant speak to HMRC and file returns for you. Until the right authorisations are in place, HMRC staff cannot discuss your taxes with your new firm, even if you think everything has been handed over.
Each tax has its own authorisation:
- VAT
- PAYE and CIS
- Corporation Tax
- Self Assessment
Common pitfalls include:
- HMRC posting codes to an old registered office, so they never reach you
- Delays in post to large London buildings, especially where there is shared mail handling
- Clients assuming the new accountant is already the agent, when HMRC still lists the old firm
The safest approach is to plan the sequence:
- Start authorisation with the new accountant well before any tight deadline
- Keep the old agent in place until you are sure the new firm is fully authorised
- Only remove the old agent once you and your new accountant can see that they appear on HMRC systems
If you hire an accountant in London close to a due date, this overlap can be the difference between a smooth switch and a last-minute panic.
Data Migration Risks with Cloud and Desktop Software
Switching advisers often means changing how you keep your records. Many people move from Excel to Xero or QuickBooks, or between cloud platforms, at the same time they change accountant.
Typical risks during data migration include:
- Only part of the historic data being imported, so reports miss older figures
- Accounts in the chart of accounts being mapped incorrectly
- Tracking categories, such as projects or locations, being dropped
- Invoice attachments, receipts, or bank statements not moving across, which weakens your audit trail
A structured migration plan might include:
- A clear cut-off date, so you know which transactions sit in old software and which in new
- Agreed opening balances, checked against signed accounts and tax returns
- Full bank reconciliation sign-off before and after the move
- Test reports, such as profit and loss and VAT summaries, run in both systems and compared
You also need safe transfer methods for sensitive data so bank details, payroll files, and ID documents are handled in a GDPR-aware way.
Disengagement Letters, Professional Etiquette, and Legal Duties
When you leave an accountant, they should send a disengagement letter confirming:
- What work they have done, and up to which date
- Any outstanding returns or filings that they will not complete
- What information they will keep, and for how long
This protects you from assumptions on both sides. It should be clear whether they, or your new firm, will file the next VAT return or payroll submission.
There are also professional duties. Your old accountant should cooperate with the new one, within reason. Fee disputes can slow down the handover, and some firms may delay sharing records if bills are unpaid, which can put you under pressure close to deadlines.
On the other side, your new accountant should issue an engagement letter that sets out:
- Which services are included, such as accounts, tax returns, VAT, payroll, and advice
- Your responsibilities for providing records and approving filings
- Target timelines and how you will communicate
- How fees, scope, and liability are structured
This is especially important when you hire an accountant in London where multiple taxes and deadlines can overlap.
Timing Your Switch Around Key Tax Deadlines
The UK tax calendar creates pressure points for both businesses and individuals. You and your advisers have to juggle:
- Quarterly VAT returns and payments
- Monthly PAYE, NI, and CIS filings
- Self Assessment returns and payments, including payments on account
- Common company year ends, often followed by Corporation Tax and Companies House filing dates
Good timing options include:
- Switching just after a VAT quarter has been filed, so your new firm starts clean with the next period
- Moving before year end, so planning can be done while there is still time to act
- Using late summer to prepare, authorise, and migrate data before the busy autumn and winter tax deadlines
To avoid missed filings during the switch, it helps to:
- Agree clearly which firm will file the next VAT return, PAYE submissions, and any company or personal tax return already in progress
- Confirm HMRC agent status for each tax before you rely on your new accountant to deal with HMRC
- Create a short written timeline so you, your old adviser, and your new adviser all know who is responsible for what and when
Handled carefully, the change of accountant can support your long-term plans rather than disrupt them, especially if you are a landlord, run an SME, or are building a business as a female entrepreneur.
Transform Your Finances With Expert Support Today
If you are ready to get clarity on your numbers and focus on growing your business, we are here to help. At MatPlus, our specialists will review your needs and explain how our services can simplify your accounting and tax obligations. Explore how to hire an accountant in London who understands your sector, then contact us to arrange a straightforward, no-obligation discussion.
