June 2022: Flying to London after a short stay in Saint-Jean-de-Luz. We will have already been to San Sebastian. Trying to figure out the easiest airport/town to fly out of. I guess SS would be a possibility, too. We will not have a car. Just looking for the easiest, most straightforward transportation option. Thanks!
Biarritz airport (BIQ) looks to be about 10 miles from St J d L Should be a reasonable taxi ride.
easyjet and ryanair have direct flights from BIQ to a London airport (STN or LGW)
Others may have a better solution, but that is one
Flying from Biarritz to Gatwick (Easyjet) or Stansted (Ryanair) is definitely the best solution.
Besides a taxi, there is cheap €2 bus from St Jean de Luz to the airport, hourly or better ("Car Express Bayonne Hendaye"), taking 40 minutes or so.