Hugmonster... believe me, the difference is chalk and cheese. Converting a UK or JAR ATPL to an Australian one is relatively simple and inexpensive. (a couple of exams + a IR renewal in any multi engine aircraft, + medical) From Australia to the UK is a different thing. Now, I don't know what validation these guys are on. However, either way, if they want to stay on beyond the 6 months I would say that they would have to do the 14 exams (minimum).
The usual 12 month validation that has been used in the past still meant that they had to do the UK exams, settle in a new country, learn new procedures and often a/c type. That ain't easy.
I am sure BE looked around for current CRJ pilots that they could employ quickly and for a 6 month contract.