In a political metaphor that had journalists covering their eyes, the man who brokered the last coalition deal has claimed the election manifestos are "a lot of public foreplay" as parties try to signal to each other what they want if there's another hung parliament.
Lord O'Donnell, who presided over the 2010 coalition negotiations as cabinet secretary, said Labour were trying to signal "what's really important" while the Tories and the Lib Dems already know "what really matters to each other" after being in government together.
He also warned that the last coalition negotiations would be "a piece of cake" compared with talks this time around, because the rise of smaller parties would throw up so many other options.
"There's quite a lot of public foreplay, if you like, and we will see what is consummated in the weeks ahead," O'Donnell, who stood down from the civil service in 2011, said.
"I think the fact is the Conservatives and Lib Dems have been in government together, they know each other very well, they know quite a lot of what really matters to each other.
"I think Labour in its manifesto is laying out what it thinks is really important."
O'Donnell said the process in 2010 was "extremely exciting" but difficult because "there weren't really many people alive who knew about coalitions".
Speaking on The Today Programme, he said his successor Sir Jeremy Heywood would have to plan for a much wider range of possibilities, including a minority government and confidence and supply arrangements with smaller parties.
O'Donnell said managing the resulting government could also be different as a fragile administration would have to avoid repeated crunch votes in the Commons which could mean fewer new laws.
He said: " was extremely exciting. You had a serious job to do, we didn't have any precedents so it was quite difficult - there weren't many people alive who knew about coalitions.
"But I think it was a piece of cake compared to what might happen this time, to be honest. That's because if one looks at the predictions, and I think [Heywood] will be starting off with predictions, they will be preparing for all sorts of options.
"This time round I think they will include minority governments and possibly some kind of mix. There could be a party in coalition with a second party but having a supply and confidence deal with a third party."
O'Donnell also said a supply and confidence agreement between the Tories and Lib Dems was drawn up last time but was unnecessary after they agreed to a full coalition.
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The formation of the 2010 Coalition
He said: "What you are trying to do is get to a stable, effective government. Where Sir Jeremy will be getting to now is not so much thinking about what options there might be but for each option how do we turn that into effective government?
"For example, they will be studying processes and tactics from the past - remember the first half of the last century there were more minority and coalition governments than not, so there is quite a lot of precedents to go on.
He added: "They will also be thinking about, 'how do we manage government when you don't want to go to the House too often with very contentious votes?' Instead of legislation, can you have other ways of doing things?
"We might have fewer laws, which I think if they are fewer, better thought-through, better legislated, could be good."