Jeremy Corbyn has said Labour could restore its historic commitment to public ownership of industry – known as Clause IV – if he were party leader.
The clause, backing “common ownership of the means of production, distribution and exchange”, was scrapped under Tony Blair in 1995.
Mr Corbyn told the Independent on Sunday Labour “shouldn’t shy away” from public investment in industry.
Leadership rival Liz Kendall told the paper Clause IV belonged in the past.
Tony Blair’s move to ditch the long-standing commitment in Labour’s constitution to public ownership, soon after he became party leader, was seen by some as a symbolic step which made the party more electable in the post-Margaret Thatcher era.
The original wording of Clause IV was replaced with a new commitment to “a thriving private sector and high-quality public services where those undertakings essential to the common good are either owned by the public or accountable to them”.
Mr Corbyn told the IoS he could consider bringing back the old Clause IV as part of a commitment to take “necessary things” back into public ownership.
“I think we should talk about what the objectives of the party are, whether that’s restoring the Clause IV as it was originally written or it’s a different one, but I think we shouldn’t shy away from public participation, public investment in industry and public control of the railways,” he said.
“I’m interested in the idea that we have a more inclusive, clearer set of objectives. I would want us to have a set of objectives which does include public ownership of some necessary things such as rail.”
Analysis by Ben Wright, BBC political correspondent
Mr Corbyn’s campaign momentum seems unflagging – to the alarm of senior figures in the party. But he says the party needs a new statement of objectives – and that could be the original Clause IV.
Jeremy Corbyn has already promised to renationalise energy companies and the railways and increase public spending on industry. One of Mr Corbyn’s leadership rivals, Liz Kendall, condemned the idea as a “throwback to the past”.
Some party donors are alarmed by the prospect of a Jeremy Corbyn win too.
Businessman Assem Allam, who donated £300,000 to Labour during the election, has told the Sunday Telegraph he would stop giving money to the party if Mr Corbyn becomes leader, saying he never backed a “dead horse”.
Mr Corbyn is one of four candidates standing in next month’s Labour leader election, alongside Liz Kendall, Yvette Cooper and Andy Burnham.
Ms Kendall – the leadership challenger seen as being the closest to Mr Blair’s policies – fiercely condemned the idea of bringing back Clause IV.
“This shows there is nothing new about Jeremy Corbyn’s politics,” she said.
“Life had moved on from the old Clause IV in 1994, let alone 2015. We are a party of the future, not a preservation society.”
Labour leadership contest
- Who are the candidates? Andy Burnham, Yvette Cooper, Jeremy Corbyn, Liz Kendall
- Dates: Ballot papers will be sent out on 14 August; voting can take place by post or online. They must be returned by 10 September. The result is on 12 September
- Who can vote? All party members, registered supporters and affiliated supporters – including those joining via a union
- What is the voting system? The Alternative Vote system is being used so voters are asked to rank candidates in order of preference
- How does it work? If no candidate gets 50% of all votes cast, the candidate in fourth place is eliminated. Their second preference votes are then redistributed among the remaining three. If there is still no winner, the third place candidate is eliminated with their second preferences (or third in the case of votes transferred from the fourth place candidates) redistributed. It is then a head-to-head between the last two candidates