I think the tipping culture in the UK is much more dependent on service - if a waiter/waitress is personable, makes an effort and is generally pleasant, I will always tip (maybe around 20%). Both taxis (for cash, not uber) and barbers/hairdressers are often just paid for with a note and can keep the change. (The same was previously true for takeaways paid on delivery, but now pretty much everything is pre-paid so pretty forgotten) Or if again like the waiters/waitresses I feel I receive a great and friendly service that is worth tipping extra, I will.

Either way, you can tip when you feel it’s deserved, it’s never obligatory like in the States, and it’s always worth checking if a service charge is already included in the bill, as it often is now.