What do I do if a contractor, who knows I am CIS registered, does not take a CIS deduction from my invoice? Basically, he just dropped cheque off for full amount, and said I should just declare the CIS payment he hasn't deducted to the HMRC myself at the end of the tax year. Can I do that?
If the work genuinely falls under CIS, he could be in trouble. Presumably he's not going to declare the CIS he didn''t deduct on his monthly return, so that will be wrong. Subsequently, his P35 will be wrong. Ultimately, if HMRC find out, the very least he will get away with is the CIS tax being taken from him, at which point he may ask you for it!!!
Sounds like this isn't an innocent mistake, I would presume that the contractor knows what he's doing and just can't be bothered to deal with it in the proper way.