Dozens of travellers returning to Bristol Airport were left stranded after a meet-and-greet parking company failed to return their cars.
Police said a "significant number of motorists had been unable to retrieve vehicles" after returning to the terminal between Friday and Sunday.
Bristol Airport said the firm involved - Absolutely Secure Airport Parking - was not connected with the airport.
The company is yet to respond to requests for a comment.
The Bristol Post reported that some customers found their "filthy" vehicles in lay-bys and fields.
Russell and Amanda Lewington, from Box in Wiltshire, called police on Friday morning after their calls to the company went unanswered.
They said dozens of other travellers who were in a similar situation had apparently booked the same service through different intermediaries.
Mrs Lewington said, when the company's owner eventually left with police to fetch the keys, he was taken ill.
She said: "People were getting more fractious but trying to stay calm because there were children waiting with us.
"Some people were returned their keys but had no idea where their cars were parked. Some found their cars in lay-bys near the airport."
After getting a taxi home, the Lewingtons eventually located their car through a WhatsApp social media group set up by another stranded passenger and collected it from a farmers' field about 15 miles from the airport on Saturday afternoon.
Lee Drinkwater, a Royal Marine from Exmouth in Devon, found his Mercedes nine hours after returning to the airport on Friday.
He said he was charged £35 by the company for 24 hours of secure parking.
"The vehicles were stored in lay-bys, farmers' fields, down dirt tracks. They were not in secure locations as advertised."
Mr Drinkwater said that up to 30 families were among those waiting for their cars on Friday.
"They were cold, tired and hungry," he added.
Other passengers took to social media to express their anger at the situation.
Writing on Facebook, Kim Price-Harris said: "Cars left in lay-bys or on farms covered in mud. They don't even know where people's cars are or their keys.
"Lots of people left stranded at the airport."
A spokesperson for Bristol Airport said: "While we have no control nor influence over the services provided by Absolutely Secure Airport Parking Bristol, our ground transportation team and on-site police unit provided assistance to passengers affected to help locate their vehicles."
Avon and Somerset Police said it was investigating but "keeping an open mind as to whether any criminal offences have been committed".