Note to Cau: You might get away with a 10% “service charge” in Media City or London. In Amsterdam, the service is exceptional so nobody minds.
But in Manchester, this wont really go down well and will alienate you from your potential future clientele.
Had I have been impressed overall, I would have made a £1k booking for my staff Xmas party, as I did in the same location under the previous management last year. This year I will find someplace else.
So overall, I think an ‘average’ is fair.
Don’t pay that service charge people. It is in fact an optional gratuity. If you don’t resist it, it will become commonplace.