"The practice of tipping began in Tudor England. In medieval times, tipping was a master-serf custom wherein a servant would receive extra money for having performed superbly well. By the 17th century, it was expected that overnight guests to private homes would provide sums of money, known as vails, to the host's servants. Soon afterwards, customers began tipping in London coffeehouses and other commercial establishments".

https://en.m.wikipedia.org/wiki/Gratuity

Tipping in the UK at restaurants has been a thing for a long time.

However it’s normally included in the bill as service charge so you just pay the bill and don’t have to decide how much to leave yourself. In London it’s usually 12.5%.

You are allowed to ask them to remove service charge from the bill but it’s an uncommon thing to ask.

Gratuity charges are what they mean. Parties over a certain size have them added, or it’s sometimes offered on the payment terminals.

Always a fixed percentage of the bill.

It's extremely common for there to be a (not really) optional service charge included where there is table service.

Since the Tudors, before the US as we know it.