Your right to compensation
If the restaurant doesn't keep your booking, you may be entitled to claim reasonable compensation for its breach of contract to cover any expenses you incurred that served no purpose.
Whether you can claim and if so how much will depend on the specific circumstances and factors such as whether it was a special occasion and whether the expenses you are claiming back are the sort that would be expected. It will be much harder to claim expenses that are out of the ordinary.
Don't over estimate any losses
You have a duty to keep any losses you have as a result of the restaurant’s breach to a minimum and if the dispute ever went to court a judge would be likely to ask whether you could have got a comparable meal elsewhere or whether the only option was to curtail the evening and claim back all the costs you incurred.
Be careful - restaurants can claim compensation too
The contract works both ways, so a restaurant can also claim compensation from you if you fail to turn up for a booking (for the loss of the profit it would have made had you gone).
But it also has a duty to to mitigate its losses and so must be able to prove that it made every attempt to fill the table.
If it hasn't lost out on custom due to you not turning up, then the restaurant can't claim from you.