Incorrect Stevie. Long haul flights leaving the UK are categorised as Band B and the tax is a fixed amount - Currently £180 for First / Business / Premium Economy or a reduced rate of just £82 for those prepared to fly long haul in Cattle Class.
The principal driver behind sector flight pricing is convenience. Consumers will pay more for faster direct flights so airlines have to discount to persuade customers to take a slower connecting flight when a direct flight is available.