Busy B,
You are missing a much bigger point:
BALPA is fighting a tiny, miniscule battle and making a big thing of it, whilst ignoring the terrible erosion of T's & C's across the board in the UK.
As for what other airlines in other countries do, I ask you this: Does the UK HMRC accept that you should get a tax free payment for whilst you are on holiday?
Do other industries where overtime is a key component of overall pay include this in holiday pay?
If they win this, it will be a minor hollow victory that within a few years will cost the rest of us as HMRC again look into our flying allowances and decide they are too generous. My Flying hour duty pay - which unlike you quote absolutely IS to pay for meals as we don't get crew food is currently tax free unlike my sector pay. The HMRC have looked into this several times at several airlines, and all BALPA will succeed in doing is winning a minor fight before the battle is lost as HMRC tax duty pay. That £600 a year will be lost in an instant.
Why waste time and money on this when airlines such as Easy are currently employed in some of the most despicable employment practices going, perhaps it's too difficult an issue for BALPA, and ignorance is, as they say and when you are not at 36,000 ft, bliss.