To the manager
At [time] on [day, date] my party of [number] ate in your restaurant. The service we received was unsatisfactory because: [describe: why the service was poor and set out how any financial loss was caused for example, we had wine spilt on our clothes which required dry cleaning].
It is my case that you were in breach of contract as you failed to use reasonable care and skill in the provision of the service and accordingly I am entitled to claim from you [the service charge which I paid under protest] [the cost of rectifying the damage described above] which was [£xx].
I look forward to receiving your cheque for that amount within the next 14 days.