It was, according to Peter Mandelson’s former ministerial colleague Michael Meacher, “the most bizarre political appointment since Caligula made his horse consul”. Michael Wills, the justice minister, once likened Gordon Brown and Mr Mandelson to “two scorpions in a bottle – only one of them will crawl out alive”. Alastair Campbell recalls in his diaries that “Peter . . . had no doubt whatever Gordon was determined to destroy him”.

The prime minister despises Mr Mandelson, knows he has been forced out of the cabinet twice, believes him to be treacherous and untrustworthy and is aware of his poisonous relationships with almost anyone with whom he comes into contact.

So he plucks him from political exile in Brussels and promotes him to the cabinet. Either this was the action of a bold politician who can forgive and forget or, according to some Labour stalwarts, the act of a desperate man who has taken leave of his senses. It certainly is risky and goes against Mr Brown’s cautious nature. But it was not rushed. The two men have been in contact for months and it appears that it was the prime minister who was the supplicant (unless, of course, that is new-era Mandelson spin). It seems that Mr Brown has reasoned that he needs more heavy-weights in his cabinet, including such a prominent Blairite, both to shore up his tenuous position and also to heighten the gap with the Tory shadow front bench.

He is trying to reinforce his autumn political message that in a financial crisis experience is everything or, as he put it, “a new era needs new ways of governing”. David Cameron dealt with that “no time for novices” charge pretty effectively in his party conference speech in Birmingham last week. Thus the prime minister came to the conclusion that the more he can fill the cabinet with experienced Blairite old stagers, the more the shadow cabinet will look like fresh-faced novices in a mad, bad world.

The only trouble is that he has chosen Mr Mandelson, or Lord Sleaze and the Prince of Darkness, as headlines welcomed his appointment yesterday. Spin and sleaze are the two words that voters spontaneously think of when given Mr Mandelson’s name. These are what we were told Mr Brown intended to banish from Downing Street. Nor did Labour loyalists want him back. When The Sunday Times polled Labour members last month, Mr Mandelson was near the bottom of a list of former cabinet ministers they would like to see make a comeback, with only one in eight thinking it a good idea.

It is possible, of course, that a different man has emerged after four years out of British politics and that he is, as the prime minister claims, a serious person for serious times. It is possible that Mr Brown himself will bury the hatchet – and on this occasion not in his new business secretary’s skull. That Mr Mandelson is an accomplished political operator is not in doubt. He will make the Tories pause, as much for the damage he has done to the Conservative party since 1994. But they will equally take succour from the belief that this is a desperate act and Mr Mandelson is trouble, as his record shows, and he will bring trouble for Mr Brown.

The stage is now set for the final act of this government. Mr Brown is getting some help from voters fearful about the economy and uncertain of Tory inexperience. But we are heading for recession, rising unemployment and the age of austerity. It may just be that things get so bad that the two scorpions sting each other to death.