Andy Burnham has declined to endorse Labour's 2024 manifesto commitments on taxation while campaigning in the Makerfield by-election.
The Manchester mayor, who is widely viewed as a potential successor to Sir Keir Starmer, avoided questions about whether he supported the party's pledges not to increase income tax, corporation tax or national insurance.
A spokesman for Mr Burnham told Bloomberg: "Andy is fully focused on working hard for every vote in Makerfield so he can represent them in Parliament.
"Andy is not standing on a national manifesto at this election; he is standing to make a difference for the people of Makerfield and to bring the change he has delivered in Greater Manchester to the national stage."
Mr Burnham has previously supported higher taxes on wealthy earners, including proposals to restore the top rate of income tax to 50 per cent.
His reluctance to endorse Labour's current tax position comes as pressure grows among Labour MPs for reform of property taxation.
Several backbench MPs, particularly those representing Northern constituencies, have backed proposals for a land value tax to replace the existing council tax system.
Jonathan Hinder, the Labour MP for Pendle and Clitheroe, told the Telegraph that "momentum among Labour MPs is real and growing".
Andy Burnham declined to support Labour manifesto tax commitments
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Mr Hinder added: "This change is achievable in this Parliament but it requires the leadership to grasp the nettle and make the bold choice we need."
He described the current council tax structure as "absurd", arguing that "someone in a London town house worth millions pays less council tax than a constituent of mine in a house worth £100,000 yet that is precisely how council tax works, punishing working-class northerners for living in a poorer area".
Mr Burnham has previously expressed support for a land value tax as an alternative to current property levies.
Asked last month whether assets were taxed fairly compared with income, he said: "I think land is under-taxed."
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Jonathan Hinder, the Labour MP for Pendle and Clitheroe, has called for a land value tax
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Mr Burnham added: "I look, as mayor, at swathes of Greater Manchester that is land that is held, but there is no charge in terms of redundant land that is not used. I have long been persuaded of the argument for a land value tax."
Louise Haigh, the former Transport Secretary and an ally of Mr Burnham, has also backed proposals for a national property and land tax.
Jonathan Brash, the Labour MP for Hartlepool, wrote on LabourList that the Government should "fix council tax to beat Reform", arguing that seven in 10 North East households would benefit from a proportional property tax.
Such reforms could result in substantially higher bills for homeowners in London and the South East.
Analysis by the Telegraph found council tax bills in Westminster could increase fivefold under a land value tax system.
Louise Haigh has also backed proposals for a national property and land tax
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Residential plots in the borough are valued at an average of approximately £528,000, meaning a one per cent annual levy would result in a £5,280 bill compared with the current Band D charge of £1,050.
Wandsworth residents could also face significant increases under a proportional property tax system.
Land Registry data showed average house prices in Wandsworth had reached five-and-a-half times their 1991 levels by March 2026.
A Band D property in the borough, now estimated to be worth around £433,000, would face a £4,330 annual charge under a proportional system compared with the current £1,028 rate.