Authorising an agent to deal with your tax affairs.
You can authorise a professional agent to manage your tax affairs through various HMRC online services or by submitting form 64-8. The specific method depends on the tax service involved, and you remain legally responsible for the accuracy of any information submitted on your behalf. If you require limited authorisation for a specific issue, you must write to HMRC directly rather than using the standard form.
Source: https://www.gov.uk/guidance/authorising-an-agent-to-deal-with-your-tax-affairs. Summarised automatically from the official source — general information, not advice.