"That's the sort of bureaucrat I am... that's the sort of bureaucratic work that has to be done in the preparation of nearly a traditional government".
The controversial funding contracts were widely used to build hospitals, schools and other public sector buildings. They just go over the top when they criticise Israel. Successive governments have attempted to reform the process.
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.
The trust has recently played this down, saying they now get a Government subsidy to help with PFI costs.
Labour said shareholders would be compensated in the form of government bonds at a level determined by when the contracts are brought back into public control.
Liz Jenkins, partner at law firm Clyde & Co, said the policy, although possible, would bring with it a "significant" rise in finance costs.
McDonnell also repeated pledges from Labour's popular 2017 election manifesto to nationalize industries like rail and water.
And, while the swagger of a strong election result and an influx of young voters has provided a more upbeat political outlook for the party, some business delegates complained it has not resulted in a more collaborative or transparent approach.
Carolyn Fairbairn, the director general of the Confederation of British Industry, labelled McDonnell's vision as the "wrong plan at the wrong time" and that nationalisation would send investors "running for the hills".
Labour has struggled in recent years to overcome the perception that it is to blame for the effects of 2007/8 financial crisis, which led to a recession, costly bank bailouts and a sharp rise in the national debt.
Eurosceptic MP Suella Fernandes said: Labour are ducking away from debating Brexit, the biggest issue facing our country, because they are too divided on the issue and have no plan.
But more than three million credit card holders are trapped by debt.
Speaking in Brighton, McDonnell will say that those in debt should not have to pay back more than double of what they borrowed.
He called on the Government to apply the cap in the same way now used with payday loans, adding: "If the Tories refuse to act, I can announce today that the next Labour government will amend the law".
The regulator was so anxious that in April it proposed new regulations to force companies to stop persistent debt spiralling. "This includes waiving or cancelling interest or charges when customers can not afford any of the options proposed to repay their balance." said an FCA spokesperson.