Under the various Sale of Goods Acts and supply of Goods and Services Act the garage that did the clutch are absolutely responsible for putting your car right. There are no get outs under these acts. So first of all don't be fobbed off.
Unfortuately, under the Acts, you have to give them a chance to fix it before you take it elswhere and bill them for it. However, it could be argued that you carried out you part of the bargain when you took it back the first time and that they failed to fix it as it has broken again. That being the case: Get a report (AA Man?), get it fixed, send a copy of the bill with a covering letter to the original garage pointing out that you 'Informed them that the job had not been carried out properly within a reasonable amount of time' when you took it back the first time.
If they refuse to pay or ignore your letter. Go to your local Small Claims Court. They are very helpful and will help you file your claim.
Terry
July 2006