Question Author
thanks for all your answers
carlton23, i have been using the plummers tape for a few days but it still gets loose and drops out again.
phoned the plumbing shop, he said it should just screw in, and told us how to remove the top of the tap, (by removing the red/blue hot /cold circle to reveal a screw) didn't even know that it was there. my husband has had a look but it just seems the thread inside the top of the tap is worn, suppose we will end up with a new tap.
thanks again everyone