Without repeating what you already know from the article the following points I would raise when considering the article.
No specific models or brands are referenced (just those which have previously been tested by Which?), but cites tests performed by Which? who do not have any a safety or electrical testing accreditation as far as I can understand have showed only those with a metal back prevent an electrical fire spreading.
That said the Fire Service have advised they are concerned with the introduction of plastic to the rear of appliances, but again havent advised any reason why they are concerned, other than they consider all Fridges and Freezers high risk since they are on 24/7 and unsupervised.
Currently the use of plastic in the construction is still within EU and UK safety guidelines, the manufacturers are aware of this article however chosen not to recall affected models or retrofit metal covers to the rear panels, so I do not believe there is any serious concern.
Looking at Zanussi there are no fridges marked as high risk or in need or recall, this list is updated regularly and can be found here.
My personal view on the situation is increased metal parts could lead to increased risk of electric shock in situations of other electrical faults, though can see potential for fire not to be retained in the appliance as well as metal panel, however the compressor and other electrics are not covered as can be seen by looking at the bottom 12 inches of the fridge so that is open to all elements, so I think this is alarmist, and detracts from proactive maintenance, such as cleaning the fridge and rear panels regularly, checking electrical cables, and fuses are fit for purpose, and ensuring there is adequate fire detection in all areas of the home.
Should you wish to discuss your concerns further the electrical fire charity can be reached at *****@******.*** they have access to a far greater source of information and can give you their impartial view too.