Senior allies of Jeremy Corbyn have warned Labour is too dominated by Remain-backing, southern members as the battle for soul of the party intensifies.

Party chairman Ian Lavery and Jon Trickett, the shadow cabinet office minister, issued a rallying cry to working class northern voters to join Labour, ahead of the registration deadline for non-members to vote in the leadership contest on Thursday.

In a veiled dig at London-based candidates such as Sir Keir Starmer, the shadow Brexit secretary, and Emily Thornberry, the shadow foreign secretary, the duo said Labour must be "rebalanced" if it hopes to rebuild its fortunes after its disastrous election defeat.

It comes as Corbyn ally Rebecca Long-Bailey came out ahead of her main rival, Sir Keir, in a new poll by LabourList, in a sign the Labour leadership race could be narrowing.

In a joint article in the Daily Mirror, Mr Lavery and Mr Trickett said: "Over the past few years Labour has become Western Europe’s largest political party and this is a welcome achievement.

"However our membership is now disproportionately one that voted to Remain in the referendum and drawn from the South, mainly from metropolitan areas and from the middle classes.

"Our decision and policy-making is increasingly informed by the opinions and experiences of those groups.

"To win again the coalition of working and middle class people within our own party must be rebalanced.

"That is why we are calling for Labour supporters from working class backgrounds and from the North to join the party by January 20 and have their say in the upcoming leadership election."

Ian Lavery, Labour's party chairman (Alamy)

Mr Lavery was understood to be considering a run at the leadership, before deciding to support Ms Long-Bailey in the contest. Mr Trickett also nominated the shadow business secretary for the top job.

The Survation poll for LabourList found that Ms Long-Bailey would win 42 per cent of first preferences while Sir Keir would receive 37 per cent.

Prominent backbencher Jess Phillips lags behind on 9 per cent, Wigan MP Lisa Nandy on 7 per cent and Emily Thornberry on just 1 per cent.

Sir Keir receives the majority of second preferences but the voters are not enough to wipe out Ms Long-Bailey’s first round lead, at 51 per cent to 49 per cent.

Ms Long-Bailey, the shadow business secretary who is regarded as the favoured candidate of the party's left-wing, has kept a low profile so far but she is expected to launch her campaign on Friday.

Candidates for leader and deputy roles face a fraught battle to win the support of trade unions, affiliated groups and constituency Labour parties to get onto the ballot paper for members.

All of the contenders must get the support of 5 per cent of local parties or three affiliates, including two unions, by February 14.

The battle to replace Jeremy Corbyn as Labour leader Show all 8 1 /8 The battle to replace Jeremy Corbyn as Labour leader The battle to replace Jeremy Corbyn as Labour leader Keir Starmer The former director of public prosecutions undoubtedly has announced that he is standing for the leadership. He is highly-regarded by both left-wingers and centrists in the party. As Labour’s shadow Brexit secretary, he played a key role in the party’s eventual backing of a second referendum. Before becoming an MP, he was a human rights lawyer - conducting cases in international courts including the European Court of Human Rights. Launching his bid, Starmer said that Labour must listen to the public on how to change "restore trust in our party as a force for good." A YouGov poll places him comfortably in the lead as the preferred candidate of 36% of party members EPA The battle to replace Jeremy Corbyn as Labour leader Lisa Nandy Wigan MP Lisa Nandy has announced she wil stand for the leadership. In a letter to the Wigan Post she said she wanted to bring Labour "home" to voters in its traditional strongholds who have abandoned the party. Nandy went on to say that she understands "that we have one chance to win back the trust of people in Wigan, Workington and Wrexham." A YouGov poll shows that Nandy is the first preference for 6% of partymembers. Getty The battle to replace Jeremy Corbyn as Labour leader Rebecca Long Bailey A key ally of the current left-wing leadership of the party, the Salford & Eccles MP is viewed in some quarters as the natural successor to Mr Corbyn and describes herself as a “proud socialist”. Highly regarded by the shadow chancellor, John McDonnell. She won also won plaudits for her performance filling in for Corbyn both at prime minister’s questions and during the general election debates. The shadow business secretary grew up by Old Trafford football ground and began her working life serving at the counter of a pawn shop. Launching her leadership bid, Long Bailey said the party needs to make the positive case for immigration as a "positive force." She also broke with Corbyn over Trident, saying "If you have a deterrent you have to be prepared to use it." PA The battle to replace Jeremy Corbyn as Labour leader Angela Rayner - Deputy leadership Shadow education secretary Angela Rayner has joined the contest for deputy leadership of the party. After ruling herself out of running for the leadership, the Ashton-under-Lynne MP launched her bid for deputy warning that Labour faces the "biggest challenge" in its history and must "win or die." She is close with leadership contender Rebecca Long Bailey PA The battle to replace Jeremy Corbyn as Labour leader Rosena Allin-Khan - Deputy leadership Shadow sport minister Rosena Allin-Khan said Labour need to listen with "humility" to lost voters as she launched her bid for the deputy leadership. Writing in The Independent, the MP for Tooting refelcted: "We shouldn’t have ignored the warning signs in Scotland, and now we’ve paid the price in northern England, across the midlands and in Wales." PA The battle to replace Jeremy Corbyn as Labour leader Dawn Butler - Deputy leadership Shadow women and equalities secretary Dawn Butler was first to announce her bid for the deputy leadership. The Brent Central MP has served in Jeremy Corbyn's shadow cabinet since 2016 PA The battle to replace Jeremy Corbyn as Labour leader Ian Murray - Deputy leadership Labour's only MP in Scotland said that the architects of the party's "catastrophic failure" in the December election can not be allowed to lead the party forward PA The battle to replace Jeremy Corbyn as Labour leader Richard Burgon - Deputy leadership Shadow justice secretary Richard Burgon is standing as a continuity candidate, flaunting his loyalty to Jeremy Corbyn and saying it is wrong to blame the current leader for the election defeat PA

Sir Keir has pulled ahead by winning the backing of Unison, the UK's largest trade union, and SERA, Labour's green group, leaving him to secure only one more union to pass through to the next stage.

Ms Nandy won the backing of the National Union of Mineworkers (NUM) on Tuesday, in a highly symbolic victory for her campaign. She is thought to be the favoured candidate of the GMB union, one of Labour's largest affiliates.

Ms Long-Bailey is expected to win the backing of Unite, Labour's largest financial backer. However Len McCluskey, the powerful Unite boss, has said no decision has been taken.