We tried everything, the crumb tray was cleaned, the fuses were checked and when the lever was held down it didn't heat. There were special "castle" shaped screws on the underside and when it was possible to remove them - standard screwdrivers wouldn't do the job, there were computer chips in it!!!!!!. The toaster was consigned to bin...problem solved. Guess trying to check out which chip was faulty etc just didn't seem to be worth the effort.
Thanks for the replies.