Most likely cause is the freezer evaporator is frozen up due to a faulty thermistor. They call it a NO FROST PROBE. Available to buy here: http://www.interspares.co.uk/product-info.php?cPath=2192_64_2399&products_id=155771&osCsid=941112d554d061afaac9ea0593fe7603
Hope this helps.
Interspares Technical, February 2009