At present there is little guidance on what is required when you call HMRC to agree time to pay your forthcoming tax liabilities.
If you are thinking of approaching HMRC our advice would be to do this well in advance, as the telephone lines are very busy. The helpline number is 0800 0159 559. Opening hours are Monday to Friday 8am to 8pm and Saturday 8am to 4pm.
You may also find the attached guidance helpful. This was prepared by our professional body, ICAEW, from past experience of negotiation these arrangements with HMRC.