Drivers who parked on the old Peterborough District Hospital site were left stranded when boulders blocked their way out this morning.
Peterborough and Stamford Hospitals NHS Foundation Trust put up concrete blocks, barring entrance to the unused car parks on the hospital site, off Thorpe Road, this morning.
But three vehicles were left stuck, despite warning flyers posted on Wednesday.
It follows two weekends in a row where travellers set up camp in the area and a meeting on Monday opted to re-open the pay and display car parking.
A spokesman for the Trust said: “Some minor changes have recently been implemented at the site, to ensure that the area is safe and secure.
“The PDH site is an asset which we have to protect. We still intend to offer car parking and any changes made in the last week should not interfere with that plan.”
The spokesman added that the owners of the last two cars were expected to return shortly and would be allowed off the site.
In the flyers put on cars it says the ‘unauthorised use of the car parks’ had lead to travellers using the site.
The trust moved out of PDH two years ago into Peterborough City Hospital in Bretton.
Details on how much the parking will cost have not yet been decided.