You will need to register as an Agent if you:
are an accountant, payroll bureau or agent wishing to use HM Revenue & Customs (HMRC) Online Services on behalf of your client(s).
an agent, whether paid or acting in a voluntary capacity, is any organisation or individual who acts on behalf of an HMRC customer who in turn can be an individual or an organisation.
To register as an Agent:
To use HMRC Online Services, you need to obtain an Agent Reference Number, which is provided to you when you register as an Agent for the service(s) you wish to use. For Self Assessment and Corporation Tax please contact your tax office. For PAYE, you can register online using the 'Agent Reference Service'.
Obtain authorisation to act on behalf of a client. There are a number of ways this can be set up. For further information see 'Get authorisation to act on a client's behalf'.