Hotpoint Mistral fridge not cooling?

Mistral FF72P - Freezer ok at -20 degC, but fridge not cooling properly. Have read other posts regarding cleaning the vent at the front (removed 3" of fluff), and removed the lower panel at the rear to confirm that the motor fan was operating (no problems there).
After completing these tasks, the fridge temperature started to drop to below 5 degC, all appeared well.
The next day, I discovered that the fridge temp had risen to about 15 degC.
Decided to remove contents of fridge and freezer (and give it a damn good clean).
In the freezer section, there's a panel that can be removed. This houses the refridgeration elements and also the cooling fan that presumably draws air from the fridge via a duct.
This fan was not running.
I thought that there may have been a build up of ice preventing the system from running efficiently, but after a couple of hours with little or no water draining to the drip tray at the base, I started to refill the freezer (not fridge) and reconnected the supply.
After a couple of hours, the freezer temperature had dropped to -22 degC, and oddly enough, the fridge had dropped below 10 deC. Just checked again, and it's close to 5 degC.


I'm not able to check whether the cooling fan is running without removing the freezer panel. I suspect it is, but why would it work intermittently?
I could really do with a service manual, but that's obviously expecting too much from the manufacturer.

Any help would be appreciated.

Andy