More than 200 cars left with Heathrow Airport parking firms were left in a council car park and issued with parking tickets.
In total, 275 vehicles were left over the Easter weekend in West Drayton, about 15 minutes from the airport.
One woman said she was "horrified" to find her vehicle was left in a public car park after she spent more than £100 for it to be left in a secure facility.
Both Hillingdon Council and Heathrow Airport have begun an investigation.
Companies offering meet and greet services meet customers at the airport then take their vehicle to a secure parking facility, and return it when the owner gets back from their trip.
When the BBC visited the council car park, some cars had up to five parking tickets on their windscreens.
Many also had Heathrow "short stay" parking vouchers inside them, which is the area where meet and greet firms pick up their customers' cars.
David and Julia O'Neill, from Lichfield, found out their car had been issued with a parking ticket after they returned from a two-week trip to Vietnam.
Ms O'Neill said the couple were "horrified to find out our car had been parked here" having been told it would be left in "a secure car park".
"We'll just wait and see now if the council get in touch about our parking ticket," she said.
In a statement, Hillingdon Council said it was "aware of reports that some vehicles were parked in the car parks" which had not been left by the vehicle owners.
"Our trading standards team has launched an investigation and will be contacting the people who have received the parking tickets in due course," they said.
A Heathrow spokesperson said the airport was working with "police and the local community to investigate this matter further".