That's slightly frustrating to hear that Kayak are getting messed about by Google, as Kayak is about the only flight search tool that I've used that suits the airport situation in the UK.

(e.g. 4-5 international airports reachable within 1 hour drive, another 2-3 reachable within 2 hours drive, flexibility to search across all of them).

The other flight search tools that I've used might, at most, allow one alternative airport.