A strange story- the chef (not the waiter or restaurant manager) complains you have taken some extra slices of meat so you give him 20 quid to shut him up - then he reports you! Are buffets really that expensive in Manchester? If it happened to me I would ask to see the manager and try to sort it out with him.
Would the chef really be able to insist the pilot was given a blood test? Normally that is up to the police or you can insist on it yourself. A policewoman friend once told me that if you fail the breath test then it is not wise to ask for a blood test as it normally gives a higher result.