Interesting article from Which regarding fire safety in fridges/freezers:
http://www.bbc.co.uk/news/business-41336234
Boils down to what the back is made of- plenty appliances out there with flammable materials close to the compressor/radiator. If an electrical fire starts here, it can get very ugly, very quickly. A fully protected metal back casing can help prevent the electrical fire becoming an insulation fire.
Some brands fair much better than others- as might be expected, the more upmarket names are in the 'safe' list, although it's good to see Beko in there too (I say that because my fridge and freezer are both from them!)
Now for my hair-brained suggestion: what about fitting an automatic fire extinguisher in the void behind an adjacent kitchen unit, aimed at the compressor? These things are standard fit in engine compartments (boats, rally cars etc) and not expensive- about £30. Would give some peace of mind anyway.