5% of GDP would be another £40bn a year. Where on earth are you going to get that sort of money from? More importantly...as Pr00ne keeps asking "what are we getting for the £40bn we already spend?" As a taxpayer you can be certain that I'm not about to give another penny willingly to the organisation that I saw waste so much that it was given over the 30 years I was watching!
I suppose the extra £40bn could at least buy some substance to go with all the gold plating that's on order.