Airlines must quickly provide clarity on which flights are being cancelled at Heathrow after the airport announced yesterday that a further 4,000 seats a day must be cut.

As 1,500 of the seats have already been sold, those trips must now be cancelled.

Which? Travel Acting Editor Guy Hobbs said the news, announced in an open letter to passengers, meant ‘thousands of people will now be worrying about whether their flight or holiday plans are about to fall apart’.

He added: “Heathrow must work with airlines to quickly provide clarity on which flights are being cut, and airlines need to be upfront with those passengers affected about their right to be rebooked at the earliest opportunity, including on services from other airlines.”

In his open letter to customers, Heathrow CEO John Holland-Kaye said that despite earlier flight cancellations by airlines, they are still scheduled to operate 4,000 more seats than the airport can handle each day between now and 11 September.

He said that 1,500 of these seats have already been sold and airlines have been ordered not to sell any more.

 “Last month, the DfT and CAA wrote to the sector asking us all to review our plans for the summer and ensure we were prepared to manage expected passenger levels safely and minimise further disruption,” he said.

“Ministers subsequently implemented a slot amnesty programme to encourage airlines to remove flights from their schedules with no penalty.

“We held off putting additional controls on passenger numbers until this amnesty process concluded last Friday and we had a clearer view of the reductions that airlines have made.    

“Some airlines have taken significant action, but others have not, and we believe that further action is needed now to ensure passengers have a safe and reliable journey.  We have therefore made the difficult decision to introduce a capacity cap with effect from 12 July to 11 September. Similar measures to control passenger demand have been implemented at other airports both in the UK and around the world.  

“Our assessment is that the maximum number of daily departing passengers that airlines, airline ground handlers and the airport can collectively serve over the summer is no more than 100,000. The latest forecasts indicate that even despite the amnesty, daily departing seats over the summer will average 104,000 – giving a daily excess of 4,000 seats. On average only about 1,500 of these 4,000 daily seats have currently been sold to passengers, and so we are asking our airline partners to stop selling summer tickets to limit the impact on passengers.   

“By making this intervention now, our objective is to protect flights for the vast majority of passengers at Heathrow this summer and to give confidence that everyone who does travel through the airport will have a safe and reliable journey and arrive at their destination with their bags.

“We recognise that this will mean some summer journeys will either be moved to another day, another airport or be cancelled and we apologise to those whose travel plans are affected.”