Electing Jeremy Corbyn as Labour leader would be a backward move that risks creating a one-governing-party state dominated by the Conservatives, David Miliband has warned.

The former foreign secretary, who narrowly lost the Labour leadership election to his brother, Ed, in 2010, is the latest in a long line of senior politicians from the New Labour era to argue against the frontrunner.

Writing in the Guardian, Miliband said he would be backing Liz Kendall as his first preference, after being impressed by her “plain speaking, fresh thinking and political courage”. His second preference is Yvette Cooper, for arguing “passionately and effectively for a positive reformist vision and against the siren calls of ‘defiance’ of the Corbyn campaign”.

Echoing the warnings of Tony Blair, Gordon Brown, Alistair Campbell, Jack Straw and Neil Kinnock, Miliband said Corbyn’s ideas on nationalisation, 7p in the pound increases in national insurance for those earning more than £50,000, and equivocation about Britain’s place in the EU, were the same policies he learned were wrong when he first joined the Labour party in 1981.

However, such interventions have failed to dent Corbyn’s status as the frontrunner, suggesting they have backfired or fallen on deaf ears among members and supporters. Ed Miliband has been facing calls from within the party to speak out about his choice, but is understood not to be planning to say anything.

Corbyn’s office has dismissed the string of warnings about his politics, saying “credibility cannot mean an orthodoxy of austerity that chokes off recovery”.

As well as public interventions, there have also been machinations behind the scenes from those determined to stop Corbyn.

A campaign source has told the Guardian that people in Kendall’s camp tried to get both her and Cooper to withdraw and rally round Andy Burnham. But Cooper refused and Kendall was not willing to drop out on her own. After a speech on Thursday, Cooper told the audience it would not have been right for the two women to give up, leaving a field of two men. Kendall denied to the BBC on Monday that she had offered to withdraw.

The Daily Telegraph also reported on Sunday night that former Labour cabinet minister Peter Mandelson attempted a “secret plot” to convince Corbyn’s three rival candidates to pull out to annul the contest.

As ballot papers begin to land on the doormats of party members and supporters, Cooper is now vying with Burnham to be seen as the candidate who can beat Corbyn.

There is now a clear difference of approach from Burnham, who has said he would work with Corbyn in an effort to win over some soft-left voters, and Cooper, who has said she would not.

In return, Corbyn said he welcomed Burnham’s “inclusive tone towards our campaign and the view is mutual – if we win we would involve Andy in our team if he was willing”.

Corbyn, the Islington North MP, surprised the mainstream of the Labour party by becoming favourite in the contest with the backing of the two biggest trade unions, Unite and Unison.

Until recently an obscure leftwing backbencher, Corbyn only managed to get on to the ballot after a number of Labour MPs lent him their nomination in order to encourage debate about the future of the party. He is now thought to be largely responsible for a huge surge in Labour supporters and members signing up to back him, tripling the eligible electorate since the election.

Now living in New York as head of the International Rescue Committee, David Miliband argued that the surge in members and supporters to 600,000 members was a large mobilisation, but that the next Labour leader will have to be convincing to the 60 million people who live in Britain.

He said the main question for the centre left is how to “combine the engine of growth and opportunity that is globalisation with limits on inequality”.

In the 1980s, Labour tried proposing withdrawal from the EU, nationalisation of the top 200 monopolies and unilateral nuclear disarmament, but the electorate “sent us packing”, he said.

“We tried tempering the package, moderating its most fanciful elements, and lost again. And again,” Miliband added, saying that it was then necessary to accept that such a programme was not only unelectable but undesirable.

He said the answer to insecurity about globalisation and political frustration was “passionate reform not angry defiance” like Corbyn and Syriza in Greece.

Miliband argues that some of the ideas Labour must embrace are: how to tackle stagnation in median wages; how to redistribute power to cities to spread economic wealth; how to modernise the education curriculum for a creative age; how to build a secure, low-carbon European energy future; how to make the welfare state an effective springboard out of poverty; and how to combat humanitarian catastrophe where it occurs and before it becomes an immigration crisis on the shores of Europe.

If the party takes the wrong direction, Britain could become a “multiparty democracy with only one party – the Conservative party – that can win parliamentary majorities” and lead to further demands for Scottish separatism, he said.