Greenman: If you drive to a paid gig you have a pretty safe bet that your insurers will call it business use. If you do many such gigs they may claim you have mislead them as to your occupation as well, enabling them to avoid payment even if the claim is unrelated to the supposed business use.

They do not need to tell you this when you apply for insurance, as (in the UK at least) insurance is a contract uberrimae fidei. This means you are under an obligation to tell them all things material to the contract, even if they don't ask.