ED Miliband has been warned that Labour will struggle to win an outright victory at the next General Election and should be preparing to go into a coalition government with Nick Clegg's Liberal Democrats.

The message has come from Peter Hain, the former Northern Ireland Secretary, who has argued that voters are increasingly "promiscuous" and that single-party government could be "the exception rather than the norm in future".

In a new section for the paperback edition of his memoirs, Outside In, Mr Hain writes: "That means Labour needs to fight harder than ever for every vote in order to win elections.

"But it also means the party must accept that coalition politics may become a semi-permanent fixture in British parliamentary democracy just as it has in local government."

The Neath MP praised Mr Miliband's leadership and said it was "realistic" for Labour to hope to govern at least as the biggest party after the election.

"The question then is: with whom? It seems likely that the 'Orange Book' LibDem leadership will be rejected by their membership. That assumes, of course, that there are sufficient LibDem MPs remaining after a probable battering in 2015."

At present, the LibDems are only polling 10% across the UK, even less in Scotland, and are sometimes placed behind the anti-EU UKIP. There are growing fears among the grassroots that the 2015 election could be disastrous for the third party.

Tim Farron, the LibDem President, made clear its activists should panic at the prospect of a wipeout in three years' time. He said: "No one is pretending the next election is going to be easy. It is going to be the toughest battle we've faced since 1992, because we were nearly into oblivion then – we nearly didn't exist."