Ed Miliband is to be told by Labour frontbenchers that he will have to resign as leader if he loses the general election next year, as they move to prevent him following the example of Neil Kinnock by leading the party to two consecutive defeats.

Amid increasing concern that the Labour leader is failing to connect with voters, MPs across the party are saying Labour would need a fresh start if Miliband were defeated. "Ed really cannot stay on if he loses – that really would not work," one frontbencher said. "He has to go if we lose," said another.

Miliband's supporters say he has a genuine passion for changing the country for the better and that he is seen by the electorate as more honest and genuine than his opponents. With Labour ahead in the polls, they caution against morale-sapping defeatism.

Certainly, there is no hint of a challenge to Miliband's leadership before polling day in May 2015, but as his team try to move on after a series of gaffes, frontbenchers are expressing private fears that the party is heading for defeat. There are private mumblings that Miliband is not a winner. One said: "Ed just doesn't connect on the doorstep … It really does not look like we are going to win."

The MPs are concerned that Miliband, who has spoken of the immense challenge of returning to government after the second worst defeat in Labour's history, would try to follow the example of Kinnock, who remained leader after his defeat in 1987, only to lose again in 1992. One former minister said Miliband could not be compared to Kinnock, who modernised the party and led a professional campaign in 1987. The MP said: "People used to say Ed Miliband was Neil Kinnock. But people are increasingly thinking he is Iain Duncan Smith. Kinnock improved Labour's standing."

The pressure to ensure Miliband would stand down highlights growing defeatism among many MPs after a Guardian/ICM poll this week placed Labour just one point ahead of the Tories, on 32% to 31%.

In an essay for Prospect, the president of YouGov, Peter Kellner, writes that there would be a "startling" improvement in Labour's fortunes if David Miliband were leader. The former foreign secretary scores 35% support as the best person for prime minister, 12 points ahead of his brother. A change of leader would see David Cameron's score crash from 33% to 23%.

One MP said: "I like Ed a lot. He is a really nice guy. But he has not managed to get a hearing from the British people. His ratings have been bad since day one and he has not managed to improve them. In fact, they are getting worse."

But others who have voiced doubts about Miliband believe he took a major step in the right direction last week when he endorsed the thinking behind a major report by the Institute for Public Policy Research. The Condition of Britain examined how Labour can pursue its historic goals of equality in the age of austerity.

Rachel Reeves, the shadow work and pensions secretary, Chuka Umunna, the shadow business secretary, and Tristram Hunt, the shadow education secretary, led a shadow cabinet fightback in support of Miliband on Friday night. Reeves told the Guardian: "I am incredibly proud to serve under Ed. It would be with huge pride that I would serve in a Labour government under his leadership. When Ed is prime minister, we will see change we haven't seen for a generation. That change will profoundly change the lives of people who, for too long under governments of all colours, have been really struggling and left behind."

Umunna urged colleagues to focus on winning back support rather than obsessing about opinion polls. He said: "It is essential that everyone uses the time that others spend obsessing about polls obsessing about doing the work we need to do to continue winning back support to win next year. Winning back support has got to be the principal obsession. You can't do that if you spend all the time examining polls.

"Of course there are going to be critics because many people now believe we can win an election and there are a hell of lot of vested interests who don't want that to happen. They started off by saying there was no vision and were roundly contradicted when Ed gave his excellent One Nation speech. Then they moved on to saying we had no policies and now they are complaining that we have too many policies. That tells you something about the people who carp and criticise from the right of British politics because they know Labour can win the election next year.

"I think people far too readily dismiss what I know from my own personal experience – that Ed is somebody people believe is honest, genuine, trustworthy and believes passionately in what he advocates. We know, in this day and age, that those are very precious commodities – never mind in a politician but most importantly in a leader. They are not commodities that the other leaders possess in the same quantity."

"We will be going into this general election, seeking to move from opposition into government, with one of the most experienced leaders of the opposition in a generation. He has more experience than David Cameron or Tony Blair had."

Umunna said he was impressed when he took Miliband on a low-profile visit to the most deprived ward in the Tulse Hill area of his constituency to talk to the family of a victim of gun crime. "That meant a huge amount to the family."

The shadow business secretary said: "I am confident the public will get to know Ed really well in the full glare of a very intense general election campaign. What they will see I have absolutely no doubt they will like."

Hunt said Miliband's support for the IPPR report showed a "substantive response" to Cameron, who was dismissed by Michael Gove's former aide as a "sphinx without a riddle". He told the Guardian: "The IPPR report is a sophisticated modern social democratic response to the age of austerity. It is not knee jerk, it is not head in the sand. It is both an engagement with a modern competitive economy and it came out the day before the latest figures revealed our public finances are shot to pieces.

"We have to make sure we are all pulling our weight to make the song sing, to knit the policies together that are there. We in the shadow cabinet have to work hard to make sure it becomes a compelling electoral offer."

But one frontbencher said: "Ed is definitely an issue. But on the doorstep you are never quite sure how far people are saying it is about Ed because they think it is about Ed or whether, if you are not comfortable about Labour, you pin it on the leader."