You say you read your contract very carefully, was the contract a company based contract, i.e. identical to all, regardless of base or was it specific to your base? It may not be immediately obvious as it will be on the companies headed note paper etc. but be absolutely certain they haven't included a small phrase or sentence somewhere that, in a round about way, states that redundancy will be first in last out at the base where the surplus occurs or that the contract is specific to base, again, probably disguised.
From the day you signed your contract until the day you received your redundancy notice did your company ever advise you that changes to the law of the land might effect your contract?
Not always, but company PLCs are sometimes crewed by a bunch of self seekers who are really only looking out for themselves, they will beat the drum when it is at no personal cost but they won't always take on the company when they should for fear it might damage their careers too.
Never had any faith in BALPA and if you think you may have a case for wrongful dismissal or breach of contract I suggest you use your own lawyer. If you win your case you can then consider suing BALPA for taking your money and neglecting your best and legal interests!