Just a quick update to this old post, given my successful results having followed it to the word.
Espares.co.uk have the part numbers given (total £40 ish) and with a bit of fiddling in the back of the freezer I managed to simply replace both sensors. Only tool needed is a pozi drive / crosshead screwdriver.
My symptoms (and therefore Google search) were exactly as per the original post, and the results are a working fridge freezer.
This forum saved me several hundred pounds on a new fridge freezer. Very pleased!
Dan, July 2008