There's little point in comparing salaries with the railways. BA is wholly privatised and the railways operate in an entirely different way. Although run privately, they are operated on a fixed-term franchise that involves paymenttto the government and a lot of the fares are set by the government not the operator.
I do however agree that they have an effective union, although this is no doubt helped by a lot of people in the UK depending on the train to get to work and therefore they get very angry when the trains are off. Very few people depend on BA for their commute, and usage is also well below that of the railway.
The concept of low cost also does not exist on the railways, and there is very often no competition at all.