I looked into this after a row with a restaurant manager over his mandatory service charge following some exceptionally poor service.
The internet told me this, so it must be true:

You don’t always have to pay the bill
If you do not like making a fuss, you can always pay ‘under protest’ and write on the back of the bill – or your credit card slip - that you are doing so. Make sure you take a copy too. This gives you the chance of claiming against the restaurant at a later date. However, if you’re talking about something like £25 for two, it’s probably not going to be worth the hassle – or accepted by the small claims court.
Another option is to offer to pay a sum you consider acceptable and give your full name and address (with proof of identity), stating why you are not paying the rest. Restaurants often wrongly believe customers have to pay for a meal whatever the circumstances.
This is not the case. As long as you have a genuine reason for not paying and you leave your name and address, you have not acted in any way dishonestly.
You have not committed an offence and even if the police are called they should not usually intervene unless it is to prevent a breach of the peace.
It is a criminal offence, though, to go into a restaurant and order a meal with the intention of not paying for it.
( tangledupinblue hairy badge with moving eyes, Thu 14 Feb 2013, 10:09, 2 replies, latest was 12 years ago)

this sounds like freeman bollocks

( Naked Ape call me Caitlyn, Thu 14 Feb 2013, 10:12, Reply)

the hassle factor is the most correct point there
nobody is going to sue over a few quid.

the bottom line is, ordering a meal is a contract. the restaurant makes an "invitation to treat" on its menu. you then make an offer to purchase its goods at the menu price. the menu supplies the goods, and you give consideration for that by paying.

if the goods aren't satisfactory, you slug it out. but you can't eat them all and then argue they were shit!
( rachelswipe with a fork, Thu 14 Feb 2013, 10:15, Reply)

Oh man, I wish I knew that.
I once bought a 'club sandwich' that was 3 slices of plastic bread with a single slice of that packet roast beef between the two bread gaps, a packet of walkers crisps and a can of coke for £9. They forgot the horseraddish, butter and salad.
( G/PP 💩💩💩💩💩&#128, Thu 14 Feb 2013, 10:24, Reply)

I got ripped off at the Science Museum on Sunday; £1.70 for a can of coke.

( Fucking hell Jeff I am not a robot, Thu 14 Feb 2013, 10:25, Reply)

It's really, really hard to win that argument if you've paid up front, though.
It's one thing to refuse to pay - quite another to get a refund
( the mighty badger Aphrodite, on a bar stool, by your side, Thu 14 Feb 2013, 10:26, Reply)

Done the latter a couple of times.
The most spectacular being a curry house on the IoW with a £2000 bill for 3 yacht crews. They took 2.5 hours to produce the starters, another 1.5 for the mains and by the time the food turned up we were all too pissed to eat it. Wouldn't have been so much of an issue but the 24 of us were the only people in a restaurant with 100 or so seats, so clearly they should have been able to cope.

So we paid about £700 for the wine and refused to pay for the food, and in the end they had to accept that. Although I doubt we'd be welcome there again.
( the mighty badger Aphrodite, on a bar stool, by your side, Thu 14 Feb 2013, 10:14, Reply)

Although, having been to the Isle of Wight once, you are surely unlikely to return anyway.

( tangledupinblue hairy badge with moving eyes, Thu 14 Feb 2013, 10:19, Reply)

Sadly, it's pretty difficult to avoid if you sail in the Solent

( the mighty badger Aphrodite, on a bar stool, by your side, Thu 14 Feb 2013, 10:20, Reply)