Interestingly, this is a situation created by previous Conservative governments. When the national rail system was privatized, lots of smaller individual train operating companies were created, each with a franchise to run different lines. They are incentivized not to cooperate with each other, because taking over another franchise, if another operator fails, doubles the size of your business.

So the employers were divided and the highly unionized employees were united, which meant that they did extremely well in negotiations. The membership overall are extremely loyal to their union leadership, because of how successful they've been in maintaining conditions and improving wages.