Time to crack open the home-made grog then!
I've been wary of "free" visits ever since my parents got a 'free visual check' from the electricity supply company. A hard-nosed salesman called round, told them that they needed a split-load consumer unit (quoting £900 to fit about 12 years ago). The salesman said the wiring was in breach of regulations (only true if it had been a new home) and dangerous without it (hmm..) And, finally, that the company could pull the main fuse if they didn't agree to the work! So much for a "free" check!
cheers, a