Osborne must address the doubts the City has about his economic credentials.

During the bank holiday weekend, an email was circulating among high-ranking City financiers with the intriguing subject heading: ‘Message from George Osborne’. It was not a hoax. An executive from a fund management firm had written to the shadow chancellor’s office asking what plans the Conservatives had to reduce the deficit, as he had not read about such plans in the newspapers. He was sent a reply — which so shocked him that he sent it to every merchant bank from London to Hong Kong. ‘It looks light on content, to say the least,’ he wrote. ‘The currency markets smell blood in the water.’

It was a classic case of a political move looking mighty stupid in the real world. A junior aide in Mr Osborne’s office — until recently a secretary working for a Tory MP — had been asked to reply to the fund manager in her own name. She started out promising to ‘set out our approach to public spending in depth’, but then proceeded to regurgitate clichés about a ‘culture of financial discipline’ and clamping down on office refurbishment. There was no hint of a secret post-election plan to reduce the deficit. The many financiers who were sent this letter would understandably conclude that there is no plan at all.

A few years ago, the Conservatives could have shrugged this off contemptuously. They have an election to win: why should they explain themselves to overexcited bankers? The reason they should is that these fund managers will have more power over the next government than any since Callaghan called in the IMF in 1976. Mr Cameron will need to borrow 20p in every pound his government spends. The investment managers will be his paymasters, and he needs them to trust him.