The publication asked Tui, Jet2holidays, Thomas Cook, Expedia and On the Beach what they were doing to inform passengers about the possibility of a ‘no deal’ scenario from March 29 next year.

Talks are underway to try to seal an agreement that allows UK airlines freedom of the airways throughout the European Union in the same way as now. However, no deal has been agreed and next summer’s programmes are already on sale.

Which? found that Thomas Cook had changed terms and conditions “to explicitly state they will not provide compensation, will also not reimburse expenses or cover losses if they have to change the circumstances of your booking, which could occur in the event of ‘airspace closures’.” The magazine also said that Tui, Jet2 and On The Beach had “failed to provide any reassurance that any information would be communicated upfront”.

The research also found that Expedia was the only company trying to offer some reassurance to travellers, telling Which? that they believed airlines would still be subject to Regulation 261/2004 and the Package Travel Directive.

Which? found however that the brand was not yet marketing holidays for the post-Brexit period.

It added that Expedia “would also not be directly responsible for providing compensation for delays and cancellations, as the customer would have to go through the airline that Expedia have booked their flights with, who may also decide to insert a ‘Brexit clause’.”

Peter Vicary-Smith, Which? chief executive said: “This uncertainty for holidaymakers is just one of the many issues affecting people’s everyday lives that need to be resolved as we move closer to the date that the UK leaves the EU. We want to work with Government and businesses on issues such as this in order to deliver a Brexit that puts consumers first.

“We want to ensure that people are supported by high levels of rights and protection – and with greater access than ever before to quality, affordable products and services. We must not miss the opportunity for the UK to improve consumer protections to become a world-leader. With control over all aspects of consumer protection the UK can and must do something special.”