Leader Jeremy Corbyn has already pledged not to sign any more private finance deals. Technological change is accelerating.
"I can tell you today that when we go into government".
The former Conservative prime minister, Sir john Major set up the PFI scheme which was also backed by Labour's former prime minister, Tony Blair and Gordon Brown, this brings an end to the Blair and Brown era.
Under PFI, a private sector consortium funds, builds and maintains a facility on behalf of a public agency, then receives payments over the term of the contract, typically lasting 25-30 years.
McDonnell claimed PFI had resulted in huge, long-term costs for tax payers, whilst allowing some companies to net "enormous" profit.
'To pay for those public services we'll close the tax loopholes and the tax avoidance scams (used) by the mega rich, ' McDonnell said.
'Over the next few decades, almost two hundred billion is scheduled to be paid out of public sector budgets in PFI deals, ' McDonnell told the conference.
"'We will deliver the funding for the Midlands Connect, we will overturn decades of neglect in the south West and we will electrify the rail lines all the way through from Cornwall all the way to London once and for all".
'The government could intervene immediately to ensure that companies in tax havens can't own shares in PFI companies, and their profits aren't hidden from HMRC.
"We'll put an end to this scandal and reduce the cost to the taxpayers".
Some credit card repayment rates are now so high that customers pay around £2.50 in interest and charges for every £1 they borrow.
Labour said the changes would work in a similar way to measures on payday loans, which came into force in 2015. He told delegates: "I am calling upon the government to act now and apply the same rules on payday loans to credit card debt. You can call it the McDonnell amendment".
McDonnell also pledged to protect the rights of European Union citizens in the United Kingdom, one of the main bones of contention between Prime Minister Theresa May's negotiators and their counterparts in Brussels, saying their treatment by the Tory government has been "brutal".
The Financial Conduct Authority (FCA) launched a consultation earlier this year to look at ways of tackling credit card debt, through requiring more oversight by credit card providers.
Mr McDonnell continued: "The value of any industry that is brought into public ownership is determined by parliament itself, and that will be a detailed assessment".
"We should never forget that we are part of that great Labour tradition and we should be so proud of it".