Lib Dem leader Nick Clegg made a tactical error during negotiations with David Cameron over the formation of the Coalition in not demanding one of the big cabinet jobs, a Labour former minister said today.
Lord Adonis, who served as Transport Secretary in the last Labour Government and was part of the team that tried to agree a deal with the Lib Dems in the days after the 2010 General Election, said Mr Clegg should have demanded the post of Foreign Secretary.
He said that Clegg made a mistake in taking the Office of Deputy Prime Minister because the real power lies with the Treasury and Downing Street.
Lord Adonis said: "It would have been an interesting question if Clegg had said during those coalition negotiations when he was in a position of maximum strength because the government could not have been formed without him... if he had said 'I want to be Foreign Secretary and there will be no government unless I am'.
"It would have been an interesting test because Clegg would have wanted something that was really difficult for Cameron to give.
"It would have been a really big ask and a really big give on David Cameron's part. That would have been 'the test' that this was a real coalition rather than what has since happened which is the Lib Dems sustaining a Conservative government with a few sops."
Lord Adonis added: "I looked on with astonishment from the other side; Clegg didn't ask for anything that was really difficult for Cameron to give."
He was speaking at the Cheltenham Literature Festival where he was promoting his new book 5 Days in May: The Coalition And Beyond.
Also speaking at the event were Matthew D'Ancona, a political columnist with The Sunday Telegraph, and Philip Collins, a former speechwriter to Tony Blair and now chief leader writer for The Times.
Mr D'Ancona said during the election campaign David Cameron and George Osborne had a "real honest discussion" about every Parliamentary constituency in the country and decided they could not win an overall majority.
"So while the public face of the campaign and the briefing was 'no hung Parliaments, no coalition' at the subterranean level was a very methodical plan for precisely that, for a coalition," Mr D'Ancona said.
Mr Collins said that he thought the most likely outcome for the next general election was another hung Parliament because of the historical decline in the shares of the vote for both the Conservative and Labour parties.
"I think it's very hard to see how anyone can assemble the numbers to win outright next time," he said.
"It is very rare for an incumbent government to increase their share of the vote, especially with one that has had to do what it's done. It is very hard to see how Ed Miliband is assembling the numbers he needs.
"It looks likely to me that the Liberal Democrats are the party most likely to be in Government next time if there's stomach for another coalition."
Mr Collins said that another coalition could change the face of British politics for a generation.
"In 10 years' time there will be people who are 28 saying they've lived their whole adult life under a Liberal Democrat government and that changes the nature of their party," he said.
"That is a slow burning change in British politics - the difference the third party is making to itself, if not necessarily to government.
"When others and the third party get as much of the share of the vote as they do, it makes victory (for the two main parties) very hard to come by.
"In our lifetime that change has been disguised by two transforming politicians in Margaret Thatcher and Tony Blair, who were able to cross the socio-economic lines and win big victories.
"None of the current leaders have got that sort of reach and my best guess would be that we are going to go through these things again."