Hi Bunty;
I feel the problem is The washer on the end of the tap has herniated through the flow hole within the tap and as you turn the tap on the mechanism is moving to release the water flow but your has remained stuck in the hole totally occluding the flow.
What you need to do is turn off the water that feeds the tap. with the water off strip down the tap and I am sure you will find when you have stripped the tap down a piece of brass looking up at you from within the tap body.
With a pair of long nosed pliers grab the brass pillar gently and pull it up and out of the tap body. It may be hard at first then it will give way and pull our. when out you will see the whole thing. on the very bottom you will find a washer or the remains of one. it could be secured in place by a small nut and washer un do the nut and washer and remove what remains of the washer. clean the brass fitting it was connected to and replace the old washer with a new one. If you are unsure of the correct sized washer take it to B&Q and ask for help. with the washer replaced clean the metal fixing the washer was screwed to and give a good coating of Vaseline and refit the parts in reverse of removal. Job done . It would take me less than 20 minutes to complete.
An very little money to do it. Best of luck.. Let me know how you get on.
Pat
December 2008