Just thought I'd add a bit more info...
August-October - 80 pigs in one stud in Somerset, either died with no symptoms or collapsed and then died, 3 pm's done - all inconclusive
November - 60 pigs in one stud near Exeter, no symptoms, all died over a 3 week period. PM's done and all inconclusive
December-January - 5 sporadically in Wales, fine one day, dead the next.
January - Bristol, can't find how many pigs were lost, but a subsantial amount, all died over night, no symptoms
January - Derby, 20 pigs died overnight, again no symptoms
January - Hertfordshire, 80+ pigs died over the course of 48 hrs, no symptoms
Will add more info as and when I find it.