I normally have the tax from my business collected through PAYE in the day job.
On previous tax returns I filled that amount into box 18.2. This year I didn't and they seem to be demanding a huge payment this month (equivalent to a year and a halfs worth of tax on the self employment).
Which is the correct way to fill in 18.2? And if it was incorrect in previous years would that mean I have overpaid or underpaid (or correctly paid) tax in previous years?
PS according to a document on the HMRC website their system checks that box automatically for online filed returns. Hmmm.