Employer Breach of Contract?

My employer made me an offer of employment which is I accepted two and a half years ago. The offer letter and contract contained a benefit of fully funded rail travel in first cl. Since starting with the company they have continually fobbed me off on this term and are now finally, after much badgering offering to buy the clause out. They have only offered me �2,000 which I do not consider is anything like what the benefit is worth? Where do I stand? I feel as though I can't kick up too much of a fuss as, being a senior manager, they will probably just make my job redundant and get rid of me