It's a pity that people with no knowledge even bother to answer this sort of question..
Start by looking here, the bit about 'implied terms'.
http://www.direct.gov.uk/en/Employment/Employe es/EmploymentContractsAndConditions/DG_1003710 9
Having read it - especially the bit about custom & practice in relationship to implied terms, then go back to your boss and explain that you consider that after 9 years, you consider that inclusion of food is an implied term of your contract of employment.
See what happens next. Either he will back down or he won't - it might. If he doesn't, you have no choice other than roll over and accept it or threaten to resign and claim constructive dismissal at an Employment Tribunal - which given the present economic environment is probably a bridge too far. You are almost certainly in the right, however it doesn't prevent an employer seeking to change your T&Cs.