Taxpayers could be on the hook for as much as £50bn under Labour’s pledge to end private finance initiative contracts and bring the schemes back under state control.

John Laing Infrastructure Fund (JLIF), a leading operator of PFI schemes, has calculated that were its £871m of UK contracts returned to state control, it would receive 86pc of their value in compensation. This works out at roughly £750m.

There are currently more than 700 PFI contracts in the UK with a capital value of £59bn. It is impossible to know exactly what level of compensation would be paid out on all this contracts if a Labour government chose to take back control of the outsourced projects. But, using JLIF's calculation as a rough proxy, which is a reasonable assumption according to experts, the bill could be as high as £51bn.

JLIF runs 57 PFI projects in the UK. It operates and maintains assets including schools, hospitals and motorways. The company highlighted the potential payout in a trading update as it spelled out risks to the business following the Labour Party conference in September, when Shadow Chancellor John McDonnell said a Labour government would axe PFI deals.

David Hardy, investment adviser at FTSE 250-listed JLIF, said: “We have had a lot of questions from investors about what it would mean for us. This was the first opportunity we have had to make clear what the impact of such a change would be.” Shares in JLIF slipped 3.4pc on the revelation.