A pro-forma payment slip – SA361 – was available on HMRC's website twice a year to reflect self assessment payment dates, to be used where the original payslip had gone astray.
The payslip has now been removed. In the spirit of the Government Open Licence, a PDF version can downloaded here should practitioners require a copy when making what will probably now be a late payment.
The client’s unique taxpayer reference will need to be shown on the form; a page on the Revenue's site enables the reference to be checked to confirm that it is a valid number.