Lord Gus O’Donnell has advised the cabinet secretary Sir Jeremy Heywood to avoid relying on one election outcome forecast come May.
O’Donnell – who played a key role in the 2010 coalition negotiations – told the Today programme that no possibility should be ruled out when it comes to the makeup of the new administration.
He also said that the current electoral landscape meant that the process of forming a government after 7 May might take longer.
He said: “I think next time it could be even messier because the share of the main parties is declining, we know that. I think my successor will need to be preparing for all sorts of possible options.
“I think it’s really important he doesn’t get into the game of trying to have one forecast, it could be minority government, it could be coalitions with side agreements with other parties.”
O’Donnell added: “It may well be that we have a single majority party – I’m not making a forecast. I’m just saying that I think it’s sensible to always do the Boy Scouts thing and be prepared for all possible outcomes."
Often called the “midwife of the coalition” for his work in 2010, O’Donnell stressed the importance of politicians working together to form a new government.
“It’s for the political parties to get together and sort out who the next government is. The civil service job is to facilitate,” he said.
He also stressed that politicians should try to take a relaxed approach to negotiations.
“Chill a little. It may take some time. It may well be [that] David Cameron may win an outright majority, in which case he doesn’t even have to go to the Queen, he just carries on. You just need to be ready for all the options.”
Speaking of his own experience of coalition-building, he said: “People were saying ‘coalition won’t work, it will fall apart in three weeks, it will be ‘weak government’.
“Actually, I think what we’ve seen is that it’s lasted the full five-year term. Whatever you might think of the government, they have been able to govern effectively in the sense of pushing forward quite radical reforms in welfare, education and health.”