if it’s one of the cheap-and-cheerful clubs a beer glass goes round for the £1 coins.
If it’s an upmarket one then £5 notes are going to be the minimum.
On a tangent, in Estonia the standard contribution is a 25 kroon bill, which is about £1.25
I’m sure that some of our Londopers will be along shortly to give you a more reliable answer, but my impression is that the girls go 'round to the patrons with a tip jar before they dance, and it is mostly coins that are collected.
I dinna think they do the whole grubby note stuffing thing over there.