Good evening and thank you very much for your question.

The timing belt drives the top half of the engine. If the belt breaks or some of it's teeth sheer, the top half of the engine will stop dead with some of the engine valves open. The bottom half of the engine will continue to spin for a short time causing the pistons to come into contact with the open valves. This will cause the valves to bend resulting in a very expensive repair.

The belt should be replaced at regular intervals as documented in the cars service booklet. I think from memory that it is every 6 years or 60,000 miles, whichever is soonest.

If you are unsure when the belt was last changed, I would recommend that you do have it replaced as soon as possible.

I think that the price you have been quoted is a little on the high side, unless the garage is going to replace the water pump at the same time, which is sometimes necessary. I would say that a reasonable price for replacement of the belt and tensioner should be in the region of £120 - £150.

I hope this answers your question.

Regards, Gary.