HMRC pauses Agent Reference Number checks until 17 November

A number of members have previously reported that they were being asked to provide their firm's Agent Reference Number (ARN) as part of HMRC security checks when calling certain helplines. 

HMRC has now confirmed that ARN checks for this purpose have been paused until 17 November 2026, giving tax advisers additional time to prepare for the changes. During this period, HMRC may still ask for an ARN in other circumstances, such as when investigating an issue on an agent's behalf. Existing security, identity and client-authorisation checks will continue to apply. 

From 18 November 2026, HMRC will resume ARN checks for businesses that are required to register with HMRC as tax advisers. HMRC has advised that all relevant firm employees who interact with them on behalf of clients should ensure they have access to their firm's ARN from that date, so firms need to consider the best way of sharing this information with the relevant individuals.

The ARN is an 11-character reference found on the front page of a firm's Agent Services Account (ASA). The reference begins with four letters, including "ARN", followed by seven digits, for example: XARN1234567. Agents who have recently applied for registration and have not yet received an ARN should be able to provide their registration application reference while their application is being processed. 

For more information on Mandatory Agent Registration with HMRC, please see our Frequently Asked Questions.