Get BALPA to push for removal of senority in all UK companies and encourage free movement of pilots between companies. If your company is shafting you then you can move to a company with better T's and C's. This would lead to companies having to compete more for there workforce.
I am in buisness aviation and our company after talking up tough attitudes to the pilots is now talking about improvements to conditions as 75% of us are job hunting.
Also an advert in pilot each month explaining the cost of undertaking a career in aviation and the current returns might restrict the numbers coming in and allow market forces to push up T's and C's.
I hope it goes well for you at BA. It would be nice if pilots in the UK could show some unity but it must work both ways and when you get to the top try and look after those lower down the ladder.