I come from the north west and was drilled by me mum to always say "and your own".......20-50p taken and everyone happy.....
Moved down to the smoke and also got stung by this - although my mate had a better tale when he got stung in an
upmarket bar in shoreditch at a double patron at about 15 quid

Although he did admit another mate was being a cock to the bar staff so probably saw this as retribution......
But in the south if you say "your own" or have a drink they will pay the cost of a full drink.......
Now if I am in abusy pub or bar I can for an extended amount of time, I use this as a tactic to get the bar staff to remember me and earn that drink.....it doesn't always work, but sometimes it does, and if they are particularly good or just have massive bangers (either sex I'm not picky) then they may get another. Or sometimes I am feeling generous.....this is less regular
Over time this has built up good rapport, but at times I have had some runt in wetherspoons take 3.70 off me for no return.....