The costs of flying in the UK compared with say, USA, Canada, South Africa etc are down to much more basic economic reasons.
Firstly, we are a very small island and don't have the commercial need to fly around as much as you do in America, Australia etc. Hence supply and demand rules will mean that there are fewer operators.
Secondly, you need to look at the overall costs of living. An operator needs to make a profit. Out of his revenue, he will have to pay salaries and rent for example. Property prices are very high in the UK (again, because we live on a small island).
If you compared the net profit margin of a UK operator and and US operator, I doubt whether they'd be much different!
Cheers
Whirlygig