He was late and needed to answer a call of nature. Andy Burnham arrived, on a close, uncomfortably sticky Friday evening, to speak amid the faded grandeur of Ipswich town hall, looking a little harassed and tired.

There were nearly 150 people sitting quietly in the hall as he arrived for a 6pm performance of a well-trodden stump speech appealing for support in his bid to be leader of the Labour party.

A small group of supporters waited by the columns of the main entrance to welcome him, but a Channel 4 cameraman shoved his lens right in the shadow health secretary’s face and the attached reporter’s quickfire questions about infiltrators and legal challenges to the future result had to be addressed first.

Then it was a run up the stairs to the doorway of the main hall and a quick look around for a place to freshen up.

“I could do with, erm … ” muttered Burnham, peering around.

A middle-aged female organiser, walking two steps ahead of him and wearing a red “I back Andy4Leader” T-shirt, absent-mindedly walked into the room and started to clap vigorously. The audience quickly followed her prompt. “Oh God, right,” Burnham said under his breath as he followed her straight in.

This interminable Labour leadership campaign has been, in Burnham’s own words, “hellish” at times. His days, littered with hustings, meetings and media interviews across the country, regularly start in the early hours of the morning and end well past midnight.

His wife and three children are currently on holiday in Mallorca and tease him with photographs of themselves having lots of fun in the sun. Yet complimentary headlines, warm commentary and “political rock star” monikers have been hard to come by for all those scrabbling in Jeremy Corbyn’s seemingly unstoppable jet stream.

It is the leftwinger, with his overflowing meetings of evangelical supporters chanting “Jez we can”, or swooning at the sight of his undershirt and Breton cap, who has been enjoying the “big mo”. But, maybe, just maybe, something is happening under the radar.

In Ipswich – a seat that Labour must win in 2020 to stand a chance of being returned to power – Burnham spoke of how 2015 marked the 70th anniversary of the Attlee administration that set up the NHS and told them that the meek and mild current Labour party would not be capable of such a feat. He attacked the malnourished social care system that left the vulnerable being cared for in 15-minute slots by underpaid, undervalued staff. And he rejected those who would inject market forces into the education system.

Burnham reeled off a smattering of strong policies, from renationalisation of the railways to ensuring that workers of all ages are paid the same top rate of the minimum wage, rather than it being graded by age.

He talked of Labour being bold, rejecting the centre-right orthodoxy, and regaining the confidence to talk about tax rather than mere cuts. And his care levy plan, under which there would be a 10% tax on people’s estates on their deaths, to fund a cradle-to-grave NHS and social care system that ensures dignity in old age, catches the imagination of most Labour members.

Andy Burnham says that he has the best chance of beating current poll favourite Jeremy Corbyn Guardian

For those who have joined the Labour leadership electorate determined to vote for Corbyn, there was probably little here to move them.

Andrew Ferguson, a 30-year-old data scientist who asked Burnham at the meeting why he should support him over the leftwinger taking the contest by storm, confirmed when approached later that he was sticking with Corbyn. “Andy is good, but not great,” he explained. “I won’t put down a second preference. It will send a message.”

But Ferguson’s take on the race does not, the Burnham camp believe, tell the whole story. While the parallel won’t be welcomed, who can forget the shy Tories who turned the general election?

Phone-canvassing results from the leadership camps do not offer an accurate take on voting intentions. There is an inherent bias towards the camp that is making the call, because the caller has to identify their allegiance and most people being asked about their intentions don’t want to offend.

But canvassing results do offer an insight into trends, and August’s results could be significant, Burnham’s camp claims. According to data seen by this newspaper, Corbyn saw a steady increase in his support between the second half of June and the end of July – but it appears that this has gone into reverse in recent weeks. And, additionally, his backers think as much as a third of the potential 610,000 electorate is now undecided. Those around Burnham believe that if they can limit Corbyn to 40% of first preferences there should be enough second preferences from Liz Kendall’s and Yvette Cooper’s supporters for their man to push himself ahead of the MP for Islington North to take the crown.

It may well be that Corbyn excites – but he may also make people nervous, and the pitfalls of a Corbyn victory are being well rehearsed in the media.

Alison Beech, 56, listened to Burnham in Ipswich, and had her head turned. “I was a bit torn and my heart was saying Jeremy and he has been challenging a lot of things, which is good for the party,” she said, “But I was a member in 1981 when the Social Democrat party split off. I think Andy is the only one who can keep the party together and offer proper policies. So I am voting for him. Yes, he convinced me tonight.”

In the car driving on the A12 from Ipswich to his 8pm meeting in Colchester (running late again), Burnham reiterated his warning about the repercussions of a Corbyn victory for Labour, and raised the spectre of that SDP moment. “I think you can’t rule out some pretty seismic changes if there is a feeling that one side of the party has won out over the other,” he said.

At Colchester Arts Centre, an old church, there is a bar, and the audience (about 250 strong) waiting for Burnham is in good spirits. They even play, somewhat preposterously, the soundtrack from the film Rocky as he walks on to the stage. The leadership candidate feeds off it and sips on a beer himself, pointing out to the audience that he “isn’t averse to a pint as you may have gathered”.

He added: “I think George Osborne will be facing me across the dispatch box in 2020 and I will show him what a real northern powerhouse looks like.”

Frances White, 17, who was sitting to one side, in the shadows of the hall, asked Burnham a question. “Everything I saw in the last election is that the Tories won on the economy, the SNP won on nationalism, Ukip won on immigration, but we stood on values and we lost. What are we actually going to say on the economy? What would be the message, because I haven’t heard it from him?”

Burnham responded: “We need a Labour vision on the economy. Yes, that starts at the deficit. Here is the difference between me and Jeremy.

“I don’t think you get out of first base at a general election unless you are trusted on the economy. But you don’t have to do it through spending cuts. With Osborne’s way we might reduce the deficit but, my God, we will destroy the fabric of communities.

“There has to be a better way, I want a balanced plan for the economy. And here is the difference: tax. Tax should bear a bigger part of the burden in reducing the deficit. What is so wrong with saying that?”

Was Frances convinced? “No. I think he might be an Ed Miliband Mark 2. And he has got the charisma all wrong. I can see he is drinking a beer, you don’t need to tell me. But I don’t want Jeremy Corbyn. To be honest, I think I will vote for Andy Burnham, but that will be despite Andy Burnham.”

At this stage of the race, Andy Burnham is unlikely to quibble with that.

CHECKING THE BALLOTS

The maximum electorate for the Labour party leadership contest is 610,000. However, even those people who have received a ballot paper, or who have already sent in their vote, may not have their preference taken into account. The Labour party is checking, and rechecking, applicants and can strike anyone out until 12 September.

■ The verification system involves Labour officials cross-checking supporters seeking a ballot in the contest with the electoral roll, lists of candidates in past elections and lists of people who nominated candidates in previous local, European and general elections.

Officials have also asked MPs to go through the lists of people seeking to register who live in their areas.

Finally, officials are scouring social media to discover whether applicants have views hostile to the aims of the Labour party.

■ The decision of an official is then sent to a panel made up of members of the party’s governing body, the National Executive Committee. There is an appeal process, but it would be highly unlikely that such an appeal would be heard before the end of the contest.

■ There may be a legal recourse for candidates in the contest under contract law if they feel the rules for the running of the contest have been breached, including the provision that only voters who subscribe to Labour values should be given a vote. It has been suggested that would-be voters blocked by the party could take legal action if they believe they have been unfairly struck off, but such a move is unlikely to be successful because the party is not a public body.

■ The campaign teams for Andy Burnham, Liz Kendall and Yvette Cooper have all pressed for canvassing returns, which suggest the voting intentions of local voters, collected by the party at the general election, to be used in the verification process. Their appeals have so far been rejected.

■ It has been reported that the Labour party has so far rejected 3,000 names. More than 120,000 people have signed up to vote, along with 189,000 members of unions and other affiliates.