Controversial thought maybe, but why should someone complain if they get a non contractual BONUS...? Some people can never be happy (in my company with a 500 quid Christmas bonus people still complained, and it is a LOT, LOT, smaller than BA).
Or, when BA doesn't make such profits, will all workers make a whip around and give the company money.
As long as both sides keep their contractual word, what is the problem. If you (as a worker) are that unhappy, the door is always open to go elsewhere and the company knows this, in times both good and bad.
35 quid voucher or whatever. I agree a fiver's voucher would take the urine but then it is better to not bother at all.
And no, I don't work for BA... but work in a land where "free Chrstmas parties, free presents and more" are expected and then people still complain...