Companies that built and run NHS hospitals under private finance initiative (PFI) contracts will have made about £190m in unexpected windfall profits by 2020 because of George Osborne and Philip Hammond’s cuts to corporation tax, research suggests.

Analysis by the Centre for Health and the Public Interest found that more than 100 PFI operators in the NHS collectively saved an estimated £84m between 2008 and 2015 and are due to gain another £106m between 2016 and 2020 because of the falling corporate tax rate.

The PFI companies are making bonus profits because the corporation tax rate has fallen from 30% when the majority of their contracts were negotiated to 19% now and is due to drop as low as 17% by 2020. Some companies may be deferring their tax liabilities to later in their contracts when the rates will be lower.

Rates of corporation tax paid by a company are part of the value for money assessment undertaken by the government when looking at whether or not to use private finance or public sector funds but this has not been reassessed since 2012.

The Labour MP Stella Creasy has been calling for a windfall tax on PFI operators at a time when the NHS is under unprecedented pressure to save money. Her campaign has been backed by the Liberal Democrat deputy leader, Jo Swinson; Margaret Hodge, Labour’s former public accounts committee chair; Caroline Flint, a former Labour minister, and others.

Creasy said PFI companies were “acting like legal loan sharks to the public sector” and should not be “getting a nice bonus from the government’s cuts in corporation tax”.

“MPs across the house know first-hand the problems PFI interest rates are causing local public budgets and there is growing evidence that PF2 contracts being brought in will be just as if not more expensive,” she said.

“With Britain desperately needing infrastructure investment we can’t leave this in the ‘too difficult to fix’ box, and with these companies getting a further unexpected windfall from the cuts in corporation tax it’s time to act. After all, if I bought a new television at a set price and then it was reduced in a sale, I would not be able to reclaim the difference, so why should these companies who are already overcharging for credit get such a bonus from the change in corporation tax?

“If the companies themselves won’t propose how to renegotiate these contracts and so a more reasonable price for the public sector, then parliament can send a strong message about our willingness to legislate for a windfall tax to reclaim some much-needed funds for our local public services.”

Creasy’s suggestion differs from Labour policy, as John McDonnell, the shadow chancellor, has proposed the bolder idea of bringing billions of pounds’ worth of PFI projects and their staff back under government control.

McDonnell received repeated standing ovations from Labour activists in Brighton as he announced at the party’s autumn conference that he would “bring existing PFI contracts back in-house”.

An accompanying press release about the PFI policy appeared to be slightly less radical than McDonnell’s speech, suggesting Labour would take the contracts in-house “if necessary”.

“Labour will review all PFI contracts and, if necessary, take over outstanding contracts and bring them back in-house, while ensuring NHS trusts, local councils and others do not lose out and there is no detriment to services or staff,” it said.

A spokesman said at the time that a future Labour government would compensate shareholders in PFI companies by swapping their stakes in the contracts for government bonds. “Parliament will assess the appropriate level of compensation at the point at which contracts are brought back in-house,” he said.

John Appleby, the chief economist at the Nuffield Trust, a health charity, estimated then that the total cost of buying out all of the PFI contracts in the NHS alone could be well over £50bn.