Engineer called today and replaced the defrost timer switch. He said sometimes they stick causing a build up of ice befind the freezer back panel. Cost of calling an engineer out to fix it would be about£110.
He said that if the same thing happened again to turn off the fridge/freezer and allow it to defrost.
This could take overnight depending on the build up of ice behind the freezer panel. Suggest you try this first before calling someone out. You may need to put towels round the drip tray at the back of the fridge as it may overflow.
Bob
July 2008