I do not live in the UK, so please take this portion with that information in mind.
In Ontario, Canada, there are multiple levels of minimum wage. The lowest of these is for liquor servers (so if an establishment is not licensed to serve liquor, the wait staff are paid the higher minimum at least). This is, of course, because the expectation is that there will be at least a few tips over the period of a shift. The thing is... the difference between the lowest and the standard minimum wage is only $1.55/hr.
However, years ago, I managed a bar for a summer. As the manager, I asked them how they thought it was best to best manage tips - and they suggested we run a "tip pool". This helped to encourage the staff to not concentrate just on "my own tables" and also to give each other a nudge if their work was flagging.
Tips were shared among the staff at the end of each service. I never took any as it seemed wholly inappropriate to do so, but by running the tip pool, our dish washers, bus boys and back of house staff also got a pat on the back for a particularly good night. If a patron wanted to give something specifically to one of the servers, if a tip was "exceptionally" high, the server in question did get that bit extra at the end of the night.
It seemed to work well for them, staff morale was very good, business was brisk and patrons were happy. I handed the reins to my assistant manager for the following summer (it was a seasonal place, only ran from June to September) but he and I stayed in touch, and he told me they did the same thing regarding tips the next year.
We never asked or demanded any specific gratuities from our patrons - but they were generous and came back often.
I, on the other hand, will not patronise any establishment that has any "gratuity/service charge/whatever" added to the bill. If I am happy with the service, I'll let the server know, and try to make a point of letting the manager know, too. Not only is it good for the server(s), it is good for the manager... bloody nice to hear something positive when your job is usually to put out fires and deal with things that aren't going "right".