Adding client authorisations
Quick answer
Use two routes: copy existing Self Assessment authorisations into the ASA if you already hold SA authority, or use the digital handshake if you do not. Adding authorisations to the ASA does not sign the client up for MTD — sign-up is a separate step for each client.
Authorisation route chooser
Which HMRC route should you use for this client?
Is your firm already authorised for this client's Self Assessment?
The two routes
Existing Self Assessment authority: sign into the ASA, check which Self Assessment agent codes are already added, and add any missing codes. This brings all client authorisations linked to that agent code into the ASA. HMRC does not show a named client list in that view — only the agent codes added.
No existing SA authority: in the ASA, choose Ask a client to authorise you, enter the client's details, copy the link HMRC generates, and send it to the client. The client must open the link, sign in with their own HMRC credentials, and approve the request themselves. HMRC is explicit that clients must not hand their sign-in details to an agent.
Digital handshake timing
The authorisation link expires after 21 days. If the client does not use it in time, create a new request. The ASA shows request history for the last 30 days, including current status.
More than one legacy agent account
If the firm has multiple HMRC online services accounts, repeat the "add existing Self Assessment authorisations" process for each relevant Government Gateway login or agent code. Partial transfers usually happen because only one legacy account was linked.
Good to know
If you add an existing Self Assessment authorisation into the ASA, HMRC treats you as the client's main agent for MTD for Income Tax unless a different arrangement is later agreed.
Related: Managing multiple agents · Client sign-up process
Related Articles
Was this article helpful?
Ready to comply with MTD?
Abridge makes it easy to submit your spreadsheet to HMRC.