From the 17th of April to the 2nd of June, the agent-dedicated line (ADL) will exclusively attend to calls concerning self-assessment late filing penalties and appeals as well as PAYE coding enquiries. The ADL will not attend to any calls regarding progress chasing.
HMRC recommends that agents utilize its online services or main helplines for all other inquiries.

HMRC has the following tips for when an agent must use post, although it reiterates that online forms are less likely to be rejected due to errors or missing information:

• use the right postcode and put the full postcode on the envelope;
• use letter headings so they get to the right department;
• put any identifiers such as the client’s National Insurance number and unique taxpayer reference (if they have one) on the first page and make sure they’re clear and prominent;
• only include supporting documents if they’ve been asked for or are needed, this includes covering letters;
• only use the word ‘complaint’ if it’s a genuine complaint;
• make sure any print and post forms are complete and correct.