The owner of Stansted Airport has escaped a £12.5 million fine after admitting that East Midlands International Airport (EMIA) had fixed car park prices.
The Civil Aviation Authority (CAA) found EMIA had flouted competition law by fixing prices with Prestige Parking Limited between October 2007 and September 2012.
However, Manchester Airports Group (MAG), which owns EMIA, has seen the penalty reduced to zero after it confessed to the Competition and Markets Authority (CMA) before an investigation took place.
Richard Moriarty, markets and consumers director at the CAA, said both firms knew they were harming competition but had failed to act.
"Competition at airports is crucial to ensure that consumers benefit from choice and value for the whole passenger journey, including for services such as car parking at the airport.
"The fact that an airport operator owns land at the airport on which an independent business operates does not mean that the airport can dictate the price of services sold by that independent business."
EMIA struck a deal with Prestige which meant the firm could only offer services if it did not undercut prices at EMIA's car park.
The CAA also found that the two companies shared information about car park prices, while EMIA "actively monitored" Prestige's prices.
"This case should serve as a clear sign that we are prepared to take action to protect consumers wherever necessary and companies should be well aware that they could face a significant fine if they break competition law," Mr Moriarty added.
MAG is the UK's third largest airport operator. It owns four airports in Stansted, Bournemouth, East Midlands and Manchester and provides services to around 42 million passengers each year.
Prestige also admitted to price fixing, but will not face a fine because it is no longer trading.