For not tipping in UK restaurant?

My family and I born and live in England UK. We went out for a family meal to a traditional pub , there were 9 of us, me my family (wife & 2 kids) my brother his family (wife 2 kids) and our Mum. Mum treated us approx £30 + a head end bill circa £300.... When we went to pay there was nothing about tip or anything so my brother suggested we should leave a tip or pay extra on the bill, my SIL and I disagreed. My pov is, we don't live in America and I don't fully know /understand why or how it works with regards to tips there ... the waiters are paid a wage afaik they're not self employed and we have a minimum wage, even if self employed , it's their choice to work there. If paying on card, I don't know/believe the waiters would get the extra tip it'll just go towards lining the owners pocket. The price (£25 for a Sunday lunch a head) would include wage etc ... other than bringing out the food and a few drinks and clean up once we've left (so they can serve more covers and business makes more ) they dont do more then what's expected in the JD...

I don't like going to the American chain restaurants where there's either an expecting and a "too" is applied on the bill or you get asked do you want leave a tip as I don't want have to politely decline.

So aitah for not tipping in UK restaurants?