I recall that Ryanair required passports on ALL flights.
BA were the most flexible - credit/bank card ...?
I don't see how Ryanair or any airline require passports on all flights as they are not required if the departure and arrival points are in the same country. In the UK that's any airport in England, Scotland, Wales,Northern Ireland, Channel Islands and Isle of Man.
Only photographic ID is required so they can see that the same person that has checked in is getting on the flight. Bank/credit cards wouldn't be any good as they don't have a photo on them.