John McDonnell says Labour could renationalise railways within five years

"We will have new structures of government. I'll be ready on day one going into government to be able to bring forward the legislation, to implement the policy," he said.

The unit would also advise on compensation to shareholders and help decide which private finance initiatives (PFIs) should be taken back into public hands.

In some cases, he suggested, no compensation may be needed.

"We will abide by the legal advice that is provided to us. If the legal advice that is provided to us is we are not obliged to provide compensation to some, then we will follow that advice," he said.

"There might be some factors in relation to some operations of PFIs in particular that could be brought forward that says actually there is no compensatory arrangements needed here."

The ambitious promise comes at a time when rail users have seen constant price rises, and another hike of 3.5 per cent is set for next year

Former Transport Secretary Lord Adonis commented when the CPI-based rise was announced in August that one in five passengers surveyed were unsatisfied with their last rail journey.

He said: "Can you imagine if one in five people coming out of a supermarket were not happy with the food they were buying?

"Passengers shouldn't be expected to pay more for a worse service."

Mr McDonnell faces growing pressure from grassroots Labour campaigners to resist Brexit - but has warned that a re-run risked "stoking far-right populism and xenophobia".

"I'm desperately trying to avoid any rise of xenophobia that happened last time around, I'm desperately trying to avoid giving any opportunity to Ukip or the far right. I think there's the real risk of that," he told the Guardian. "We're not ruling out a people's vote, but there's a real risk, and I think people need to take that into account when we're arguing for one."

As Labour tries to recover from the row over anti-semitism in its ranks, the party has put equality centre stage at the Women's Conference, prefacing the main conference with a special event today.

Shadow women and equalities secretary Dawn Butler has unveiled plans to establish a standalone department for women and equalities with a minister at the Cabinet table in a future Labour government.

She will tell the Labour Women's Conference today that equality would no longer be considered an "afterthought" under a Labour government.

"So far we have seen seven different ministers for equality tagged on to four different departments and a budget that's nearly been halved," she wrote in a speach.

"This proves the Tories are not taking equalities seriously. By establishing a Department for Women and Equalities, Labour will ensure equalities is the common thread running through its government.

The main conference is expected to be dominated by squabbles over Brexit and the future of the party.

Jeremy Corbyn has also resisted pressure over a second referendum - believed to be waiting for the row within the Conservatives to spark a general election.