Mark Oaten, who appears to be trailing in fourth place, said that an e-mail, apparently showing how Charles Kennedy was helping his campaign, was removed from his office and leaked to the media.

The row intensified as Mr Kennedy’s closest aide accused Mr Oaten’s own team of being behind the leak in an attempt to boost his chances by claiming that he had the former leader’s backing.

The dispute broke out after the publication of an e-mail to Mr Oaten from Anna Werrin, the former leader’s closest aide, telling him that Mr Kennedy had approached the MPs Mike Hancock, Bob Russell, Paul Keetch and David Heath, asking them to nominate him.

Mr Oaten issued a statement saying that e-mails were removed from his Commons office and leaked “without my authority, by a person or persons unknown” and said that he had reported their theft to the police and Commons authorities, who were investigating.

In a message to party staff yesterday, Ms Werrin denied emphatically that Mr Kennedy was helping his campaign, saying that he offered to help Mr Oaten to find the seven MPs required to nominate him to encourage a contest. Mr Kennedy would not support any candidate, she said.

Ms Werrin wrote: “I can only assume — though it causes me considerable distress and anger to do so — that some bright spark on Mark’s campaign thought it would boost his chances if it looked as though he had Charles’ backing.”

The row came as Sir Menzies Campbell steadied his own leadership campaign to lead the Liberal Democrats with an assured performance at Prime Minister’s Questions yesterday after overhauling his preparations for the Commons clash. He cleared more than an hour in his diary the previous day and booked a meeting room to allow an expanded team of advisers to sift options for issues on which he could grill Tony Blair.

Having whittled down his choices, Sir Menzies then repaired with a much smaller group yesterday morning to Charles Kennedy’s former office just above the Commons chamber to put finishing touches to his questions.

Shortly before noon Sir Menzies popped into the office of Andrew Stunell, the Lib Dem Chief Whip, for some final moments of calm until he entered the Commons chamber.

The questions he asked, on rules to prevent sex offenders from working in schools, were chosen from among more than a dozen suggestions from his campaign team and party staff. But his typed notes, annotated with notes and underlining in fountain pen, included a “reserve” set of questions on the costs of the Government’s proposed identity cards scheme for use in case David Cameron, who is called first, shot his fox.

Sir Menzies’ supporters, who were visibly relieved at his performance, after Mr Blair was twice unable to answer him, said that the biggest change from his preparations a week earlier was in allowing him time to collect his thoughts. His opening questions as acting leader were rehearsed on the day in the hive of activity that was his modern Commons office in Portcullis House.

This time staff booked a meeting room on Tuesday for an expanded team of advisers, who were told to switch off mobile telephones as they sifted through a list of suggested questions, which spanned Iran’s nuclear programme to the Child Support Agency. Those present included the MPs David Laws, Nick Clegg and Jeremy Brown, plus Baroness Barker, Neil Sherlock, a public affairs adviser, and party officials. In addition to subject material, they agreed on shorter questions to maximise impact and reduce the risk of hostages to fortune.

Once a shortlist was chosen for him to reflect upon overnight, his team left Sir Menzies alone rather than come forward with further ideas or refinements and a much smaller group helped him to hone the questions early yesterday.

One of his backers claimed that he had the support of 29 MPs, taking him to the brink of a majority in the 62-strong parliamentary party, plus a majority of Lib Dem peers, MEPs and MSPs.

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