Guys:
BALPA should be able to help with the legal side of this; that is what they are therefore.
Talking to a labour lawyer on the continent, his opinion is that under EU rules management can not unilaterlally withdraw benefits that reduce T's & C's. If the benefits have been in force for a period of time, even if they are not mentioned in writing, then they are considered to be the norm. They can only be removed by mutual consent. They can not be withdrawn, whilly nilly, at the whim of management. First they would have to show just cause, in any case.
It strikes me a simple labour law matter to confirm if this is correct in UK.