Buses to the airport are stupid imo.

Realistically how many people a day from Durham are wanting a bus to the airport? The vast majority of people will drive or jump in a taxi as it's a once in a bluemoon trip and the £40 taxi is a drop in the ocean to the £2k spent on the holiday.

Either way jumping on a train for 15 minutes, then jumping on the Metro would be a hell of a lot quicker regardless.