I understand the 280fx's coming from the Chilean Army were used as primary and instrument trainers. In the US, it can be a real issue to get ex-military helos re-certified for "normal" catagory operations, particularly if the helos come from a "foreign" (non-US) military service.
In the US, some of the applicable information is...
AC21-13, AC20-96, AC21-12B, and perhaps AC21-17. I think FAR 21.185(b) comes into play also. I can't find it right now, but I've read that "foreign" surplus military aircraft might not be certified. Maybe someone with more knowledge can shed more light on this subject. I bring this up since these helos are coming from a "foreign" military service relative to the UK.
FAA Advisory Circulars
I think md600driver is correct, these machines appear to have been manufactured as normal production 280fx's when sold to the Chilean Army, so they should be re-certifiable as "normal" catagory aircraft (or the UK equivalent). I just hope the non-UK military surplus thing is not an issue.
(edited for a typo)