The Civil Aviation Authority (CAA) says it has “significant concerns” about the failure of budget carrier Wizz Air to settle court-ordered compensation payouts and delays in paying passengers what they are legally owed.

Last month, it was revealed that the Hungarian low-cost airline had racked up hundreds of county court judgments that disgruntled passengers had won against Wizz Air. Still, the carrier was allegedly failing to settle the court orders.

Many of the judgments remain “unsatisfied” because the carrier’s British subsidiary was seemingly claiming it didn’t actually have any presence in the United Kingdom and was, therefore, not bound by the County Court claims process.

The CAA revealed on Friday that Wizz Air was “clearly” ranked as the worst airline for passenger complaints, with 811 recorded complaints per million passengers. This is more than double most other airlines, with the exception of Royal Brunei Airlines which still only has 555 complaints per million passengers,

After failing to settle judgments made against the carrier, bailiffs have been sent by the courts to seize cash or assets from the airline, only to find Wizz Air UK doesn’t actually have any staff, offices or assets at its registered address.

“The UK Civil Aviation Authority has been clear with Wizz Air that this is an unacceptable way to treat passengers and that it is imperative for the issues to be tackled urgently,” the CAA said on Friday.

Anna Bowles, Head of Consumer Policy & Enforcement at the UK Civil Aviation Authority, said she had told Wizz Air to resolve overdue complaints and claims in time for Christmas in just over a weeks time.

Wizz Air has apparently “expressed regret” to the CAA over its complaints and compensation procedures and has promised that it will clear the backlog of claims and payouts.

“We understand the payment of County Court Judgements may continue into January, but we are encouraging Wizz Air to ensure that the payment of these is also prioritised,” Bowles continued.