Peter Mandelson has told the Observer that he and Prime Minister Gordon Brown have put their differences behind them and the pair are now “joined at the hip”.

But that didn’t stop Conservative leader David Cameron enjoying a joke at Mandelson’s expense on BBC TV’s Politics Show.

Put on the spot, an embarrassed-looking Cameron admitted that Conservative wags had named a unit of time after the newly-appointed Business Secretary’s surname.

The Tory wits define it as the time it takes between meeting the former EU Trade Commissioner and him saying something rude about Prime Minister Gordon Brown, Cameron confirmed.

“The point is that everyone who knows Peter Mandelson who has bumped into him recently has heard that he doesn’t always have great things to say about the prime minister,” the Tory leader said.

Taking note of the apparent rapprochement between two of the architects of New Labour, Cameron added: “A Mandelson will probably get a bit longer now.”