In between Stansted and Gatwick airport UK where is a town to have lunch It must be on train or bus route?

There are essentially two ways to get between Stansted and Gatwick by coach or train; you can either go around London on the M25 orbital motorway or through London. If you go on the M25, then there is little opportunity to stop - the National Express coach stops at Heathrow on the way, but I wouldn't suggest Heathrow airport as a lunch stop! It looks as though your best bet is to go by train to London from Stansted; you arrive at London, Liverpool Street. You then have to cross London by underground (subway) to get to London Victoria and then get the train to Gatwick. There are plenty of places for lunch in Liverpool Street or Victoria. The train fare will be around £35 for single, the coach fare around £28.