Wife had to make a TAX return this year ...
... went through all the online forms which seemed to be fairly clear and easy but the assessment came out at £200 more than it should have been. The discrepency was the amount that had already been deducted from the state pension, didn't seem to be anyway to correct that on the forms (will sort out a rebate later). Then when it came to make the payment it shunted us off to some other website where the information was not clear at all, they wanted a reference, gave a description of what it should look like, and next to the description something that looked like it was an example.
No where did it say "here is the effing number you use" so we ended up making a phone call and navigating the call centre to find some one that could point out where the information was. They didn't seem to have any idea as to what page we were actually looking at on the screen, and had us go though some other mechanism to navigate to another part of the online tax system where they knew the reference was.
HMRC have always been helpful, but last year they just seemed as lost as everyone.