Sometimes the freezer drain hole can ice up or the non return valve at the end of the drain tube can block up both these cause the water to back up then in turn turns to ice jamming the fan in the freezer so check the fan is operating if it is it could be the defrost element or cut-outs that have caused the evaporator to build up into a solid block of ice therefore restricting the airflow
We have today emptied the fridge/freezer and switched off and will leave for 24hrs to thaw out any possible blocks.
Have checked the drain tube and removed the valve, does not appear blocked and 3hrs after switching off we have a small drop of water in the container.
Tha fan appears to work, as it seem to have been operating continuously since all this started, I suppose it is because the fridge is warm and is calling for cooler air, when I open the fridge door it stops which I assume is how it should be.
Any further thoughts if this should not rectify the problem would be appreciated.