Just got back from giving it a run, drove it over 2000 rpm for about 10 mins and the light went out, what a relief!
My theory also was the cold temperatures not letting it get hot enough.
With the cost of diesel I have been driving more sensibly so not really had her up in the revs which I'm sure hasn't helped as I do a 20 min stint on the motorway daily, oh well will gave to go back to doing 80mph everywhere.
Will look into preventative measures more closely.