Yes, I get that......BUT if you are mad busy and quote eg 10% more thats fine. But not once you have the customer on the seat.
You have to be pretty stupid not to realise that in the UK there will normally be a minimum of 10% service charge added onto or assumed will be added to the bill. they aren't increasing the price once you've sat down, as you infer.
I have no grumbles about paying a service charge / tipping provided the service was fine. as mentioned, it sometime takes a bit of working out whether its included or not.
My main bug bear is a number of places don't add it on and then tap the exact amount into the card machine and there then isn't a chance to add on a tip. If you only have a £20 note and for £25 bill that can awkward
. I also hate those places where 10 /12% is added onto the bill but the card machine is then thrust at you with a "add gratuity" option open in front of you.
On the rare occasions there has been a food issue, I would look to get that knocked off the bill but still add a tip, as that isn't the waiting staff's fault.
I dislike the US model where 15-20% tips are expected to make up for poor wages, which is out of sync with Europeans expectations. I also hate the false fawning of some hospitality staff, with a have a nice day but a shitty scowl if you actually ask them to something
.