Being in the UK is ok, I'm there too. LOL.
OK, the first thing to do is just do a manual defrost, ie, turn the machine off, 24 hours with the doors open. This will clear the evaperator in the freezer.
Turn it back on and if it starts working again then the initial post here from Bryan will be on the right lines.
There are 3 parts associated with the defrost function.
The first is the pcb, this controls everything.
The next is the defrost heater and the last the defrost thermostat.
I would suspect the heater (or thermal fuse if fitted) is open circuit.
This means it's not defrosting properly and ice builds up on the evaperator. Once this the fan is unable to circulate the cold air so the freezer gets warmer.
Carry out the manual defrost. See how it goes and let me know.
Good luck with the diagnosing.