Tipping is not optional:Family locked in restaurant by staff after refusing to pay gratuity after bad service | Mail Online.

Fucking bollox it’s not optional. You don’t tip the bus driver but we tip a taxi driver. When I done charity work voluntarily, I was rarely tipped when doing house clearances. You don’t tip the gas man or any other workers that do work in your home. The restaurant at Wishaw Golf Club keep the tips and use them to help pay the staff wages. In other words, the staff don’t see the tip anyway. That restaurant is not alone. Restaurants should pay a decent wage and tipping is for when staff have provided service over and beyond the usual. You should also ask if the tips are shared among the staff equally or whether the staff keep their own tips. For example, if the food is crap but the service is good you wouldn’t want to tip the chefs for the waiting staff‘s service. And vice versa.

On top of that, if the food is sub standard, you can refuse it and pay only for the replacement, assuming the replacement isn’t sub standard. You can demand a refund for dishes that were sub standard. Most decent restaurants will not charge for dishes that are sub standard as goodwill gesture even if you ate it.