It was spent on one of two things Jay: debt interest, or Irish bank bailouts. Difference is we'll get it back which may not be the case with our Scottish generosity.
Didn't have much of a notice on lending to the Irish at that time. Either we did, or they go bust. Biggest creditor of Ireland is the UK so we would also have gone bust. Not dissimilar to an armed robbery, so can't really blame the govt for handing over the cash. It was that or lose all of ours!
This explains the problem nicely
http://www.bbc.co.uk/news/business-15748696