Any intervention in Syria is a matter for the UN, not a minor power like Britain

Why does a minor power in the world like Britain believe it should be leading the charge to military intervention in Syria? I know Briton's have an aptitude for historical amnesia but surely the Iraq and Afghanistan debacles are fresh enough in everybodies mind to be wary of another such venture. This is all leaving aside the great austerity backdrop, which apparently disappears as a matter of any consequence, when it comes to intervening in other people's countries. If there is to be any intervention in Syria it must be entirely via the UN, not at the behest of a former imperial power struggling to come to terms with its new status in the world.