As far as I can see if you have written records that prove your income, in my case my diary, then how can they argue with that? I will happily provide them with the names and addresses of my tutees, although I do wonder about data protect issues. The tax man is more than welcome to quiz the families involved but I bet they won't get a very coherent answer. Whilst I realise there are a lot of people running a full time job and private tutoring in the evenings that's their problem if they get caught. It's also their problem if their school find out that they use school resources for this private work. I'm never short of work so whatever they do doesn't cause me any problems.