Even then I'm sure they are sent over TLS.

Right, so either the airport is running something that can break TLS, or snapchat is feeding a stream of private messages to the government with ___location information provided.

Almost certainly the second.

Probably a root certificate that you need to install to browse on the airport wifi.

I’m not saying this doesn’t happen but I can’t remember ever having been asked to install a root certificate when joining an airport wifi. And I am confident that this has never happened when I’ve flown out from Gatwick.

Perhaps the GCHQ have a backdoor in snapchat then, which is comforting

snapchat uses certificate pinning so i dont think this would work anyways