The boss of Wizz Air is facing a backlash from unions, including pilots' representatives, after he urged fatigued staff to go the "extra mile" as the industry battles flight cancellations caused by staff shortages.

Jozsef Varadi made his remarks to workers after the company warned of fare increases ahead following the publication of financial results on Wednesday that showed pre-tax losses of £546.5m for its last financial year.

A recording, obtained by the European Cockpit Association and apparently edited, showed Mr Varadi criticising staff for calling in sick - contributing to its own recent shortages.

"I understand that fatigue is a potential outcome of the issues but once we are starting stabilising the rosters, we also need to take down the fatigue rate", he told them.

"I mean, we cannot run this business when every fifth person of a base reports sickness because the person is, is fatigued.

"We are all fatigued but sometimes it is required to take the extra mile."

"The damage is huge when we are cancelling the flights, it's huge. It is reputational damage of the brand and it is the other financial damage, the transactional damage, because we have to pay compensation for that."

The staff shortages are an industry-wide consequence of the COVID-19 pandemic that saw airlines and airports forced to cut staff as travel was all but shut down.

Now both are looking to ramp up capacity, they do not have enough workers and complain that security clearances for new workers are taking too long to complete.

The union responded to the CEO's remarks by demanding the European air regulator investigate the comments, adding: "It's like handing the car keys to a drunk driver".

There are rules governing the number of hours that air crew - pilots and cabin staff - can legally work to ensure safety.

Balpa, the UK pilots' union, took a similar tone in its response.

Its general secretary, Martin Chalk, said: "We know that airlines have just had the worst two financial years on record, but safety must come first no matter what.

"An airline CEO's priority is to safely operate flights that make the airline money. If you forget your safety obligations, you can forget the rest.

"No one wants fatigued pilots at the controls - the possible consequences are too devastating."

He added: "I would urge Mr Varadi to swiftly clarify that Wizz Air would fully support any pilot who does the right thing by not flying if they feel fatigued, for the safety of their passengers, crew and aircraft.

"I urge him to be as professional as his pilots in seeking to eradicate fatigue from the flight deck."

Wizz Air said in a statement that safety would never be compromised.

"Our crew unavailability has been very low, at 4%. In this context, going the extra mile to minimise disruption was discussed."

It added: "This clip has been edited from an all staff briefing - not pilots only, but also cabin crew and all office employees - on key business updates and current challenges facing aviation."