Airlines including Wizz Air and Ryanair owe millions of pounds to passengers from unpaid refunds and expenses, according to an investigation by the consumer group Which?.

It called on the government and regulators to take urgent action over the £4.5m it calculates carriers owe in county court judgments (CCJs), describing the current enforcement of air passenger protections as “fundamentally flawed”.

Which? criticised “weak regulations” and a “dysfunctional dispute resolution system” for failing to help passengers enforce their rights.

Consumers can pursue payments through county courts if they believe that an airline has failed to meet their legal obligations. CCJs can then be issued to the company requiring them to pay the passenger.

Rocio Concha, Which? director of policy and advocacy, said: “The scale of court judgments piling up against major airlines is a result of a system where the odds are stacked against passengers and airlines feel empowered to routinely ignore their legal obligations to pay out refunds and compensation.”

Wizz Air accounts for almost half of the total amount owed, according to the consumer group’s analysis of the Registry Trust, a log of court documents and fines in England and Wales.

In December, the Civil Aviation Authority (CAA) raised “significant concerns” with Wizz Air over its high numbers of complaints and delays in paying passengers what they are owed. The airline blamed the “unprecedented level of disruption” during the pandemic and said it was “putting measures in place to ensure we are better prepared, including more customer services resources and revised processes”.

It has settled more than 400 CCJs since December, it said, adding that the outstanding cases were mostly related to not receiving judgments from courts “due to problems receiving post”.

A spokesperson said: “Online registers do not provide us with the information required to settle a case. We must, therefore, write to individual courts to apply for information about each case when we are made aware of it, and then wait to receive that information. This all makes for a complicated and time-consuming process.

“We are taking this matter extremely seriously, doing all we can to fix these issues and settle all outstanding cases as quickly as possible. Customers can contact us directly using our website or app to provide information about an outstanding judgment.”

Which? called on the CAA to be more “transparent about its enforcement activities”.

Anna Bowles, head of consumer policy and enforcement at the CAA, said: “Airline passengers should rightfully expect to be treated fairly by airlines, and to have their complaints and claims resolved in a quick and efficient manner.

“We’re already reviewing Wizz Air’s performance and have expressed significant concern with them over high volumes of complaints and delays in paying passengers what they are owed, and made clear that it is not providing an acceptable level of service.”

She added: “Our latest data on airline complaints will be published shortly, along with any further steps we plan to take if service has not improved.”

The Registry Trust dataset shows that Ryanair has 840 outstanding CCJs, totalling £549,892, and Tui Airways has yet to settle 313 CCJs, worth £1.26m. British Airways has 82 outstanding CCJs adding up to £96,042 while Jet2 has four, totalling £1,434.

EasyJet owes £611,436 on 884 outstanding CCJs while Tui Airways owes £1.26m, on 313 CCJs, according to the data. EasyJet told Which? it had paid the money but the register has not been updated.

A Tui spokesperson also said the figures listed were not necessarily still owed. “In most cases it is indicative only of the record not having been updated to show payment,” they said. “Tui Airways will be taking steps to address the record.”

The airlines are members of the AviationADR resolution scheme, except for BA, which is a member of the Centre for Effective Dispute Resolution (CEDR), and Jet2, which is not signed up to a scheme.

A spokesperson for the CEDR said: “We take our duty to provide independent and impartial ADR to consumers and companies alike very seriously.”

AviationADR, Ryanair, Jet2 and BA were approached for comment.