ANDREW & HILARY MEREDITH
It sounds like the washer may have become detached. You need to undo the tap to check. It will probably need a new washer because the old one has most likely split. Just remember to isolate the supply first! That could mean finding the stop tap, or instead there may be an isolator on the tap supply. But if that is behind the bath panel it could be easier to use the main stop tap: check accessibility.
