Leigh I think its very important that we stick to what we know and also what we are qualified to do. I dont think it matters whether or not the insurance company would be happy for a 'DI' to carry out the annual inspection. They are not in a posistion to know what a DI is so I dont see how they can morally make the decision.
I have done a similar course to you so I'm not having a go, just saying that the DI course is solely for work in domestic premises and that is what we should stick to. It was made very clear to me that if a premise is commercial but with a dwelling above then I would be able to carry out work on the dwelling but not the commercial part.
Apart from the fact that we are not qualified for commercial.. If anything did go wrong I doubt your public liability insurance would be valid and also I expect you would have a pretty tough time in court!
Steer clear of it chap, I know the annual check thing sounds lucrative but it's just not worth it!