Hospitals across the south and south east are reportedly earning among the country's highest amounts from car parking charges.
A study by the PA new agency found one in three hospitals in England put up the cost of parking last year, with patients and visitors objecting to the "exorbitant" prices. The study showed hospitals made more than £254 million from parking in 2018/19, as patients and visitors said they felt ripped off.
For the investigation, 7,883 patients and visitors who had used a hospital car park in the last two years were surveyed, and financial data was gathered from 144 NHS trusts.
Frimley Health NHS Foundation Trust made £4,962,583 in 2018/19 but officials say the money is reinvested in hospital security and site maintenance.
East Kent Hospitals University NHS Foundation Trust made £4,740,464, while University Hospital Southampton NHS Foundation Trust's figure was £4,239,851.
As part of their election manifesto pledges, Labour has vowed to scrap all hospital parking charges, while the Conservatives say parking will be free for those in greatest need, including the disabled, parents of sick children staying overnight, staff working night shifts and those regularly needing outpatients.
Only England's hospitals routinely charge for parking - car parks are largely free in Scotland, Wales and Northern Ireland.
"Charges for car parking at hospitals are a charge on people who are unwell, levied on them because they are unwell. We believe that patients should not be effectively charged for being ill.
"Car parks are expensive to run for the trusts that own them.