Our problems are not over just because US Congress has swallowed hard and sanctioned sufficient tax rises to avert a plunge over the fiscal cliff. Or so the argument runs.

Sceptics - and there are plenty of them - say the deal has merely postponed negotiations over spending cuts and the government debt ceiling for two months. US Treasury Secretary Tim Geithner says the federal government would run up against a debt ceiling - a legal cap on its total borrowing set by Congress - by the end of February.