Personally, I don't believe a decline in BA pilot's T&C's will have a significant effect on the majority of pilot T&C's in the UK whatsoever...certainly not in the short to medium term. It might if you're VS, AF, KLM or LH...
In the 80s when I worked for a company other than BA. In one 12 month my pay went up by just over 50%. We enjoyed a payrise every couple of months. Why? We were rapidly expanding and could not a) recruit enough people and b) were losing experienced people to better airlines. I left too!
This was at a time when after many years of no recruitment airlines were in need of more pilots. Had the conditions at BA been equal to the airline I worked for I doubt the management would have felt the need to keep giving unasked for pay rises because people would not have been tempted to leave!
Simple market forces would indicate that in times of need the employer with the perceived best Ts & Cs will attract the most people. For that simple reason there has to be a trickle down effect from a large and high paying company to cause smaller companies to raise their game to attract and retain their pilots.