Contacting HMRC.
HMRC has paused Agent Reference Number (ARN) checks for tax advisers until 17 November 2026. These checks, which verify registration for an Agent Services Account, will resume on 18 November 2026. Tax advisers should ensure they have their 11-character ARN ready for use from that date.
Source: https://www.gov.uk/guidance/tax-agents-handbook/contacting-hmrc. Summarised automatically from the official source — general information, not advice.