Alistair Darling did something rather strange recently, to baffling applause from his own backbenchers, and cries of “bribery” from the opposition: he announced a tax on teenagers.

Darling’s plan – for those who missed it – is to cut income taxes temporarily for all but the most prosperous taxpayers. The apparent windfall is £120 a head. A similar plan is already in place in the US, where a temporary “tax rebate” began to arrive in the bank accounts of a grateful nation about a month ago.