I had the same problem with a Hotpoint FFA90 Fridge/Freezer
and almost incurred a big call out charge but was mystified by
the slow onset of the problem. After re-reading the user bumf
I decided to remove all goods from the freezer and store them under blankets in acool place. I then switched freezer off and
left it off for a few hours to allow all ice behind rear panel to
thaw and then put all food back and powered it up again.
Next morning all was well and fridge compartment temperature
was as it should be.