The car park operator has admitted the problem after it was raised by duped drivers in Lincoln.
Simone Riley-Young and Matthew Treacy were accused of staying over the permitted two hours at Tritton Retail Park in Lincoln, but both drivers noticed the times on the photos of their cars were wrong.
The same issue was also reported in Newcastle-under-Lyme, Staffordshire.
UKPC has been reported to Action Fraud and the complaint is currently being assessed by the National Fraud Intelligence Bureau.
In a statement, UKPC said: “We regret to confirm that a limited number of pictures of vehicles, at a small number of car parks, have had their timestamp altered by a few of our employees to make it appear as though the vehicles had over-stayed when this was not the case.
“We have taken this issue extremely seriously and decided that even though a number of the relevant parking charges are likely to have been legitimately issued, we will refund all potentially affected parking charges for over-stays issued by these employees, to ensure that there is no room for error.”
Student, Jade Beeby paid a £60 charge despite knowing she was not at Tritton Retail Park at the time UKPC claimed.
She said: “I was really angry and annoyed with them because I knew it was my birthday and I was with my fiancé but I couldn’t prove it.
“All I remember is that they keep pushing you to provide evidence of where you were at the time, which is hard to do if you, for example, were in bed.”
The period of time for which this has been happening has not yet been disclosed but the British Parking Association are also investigating.