EasyJet, Britain's biggest budget airline, has moved its planes from the UK to Germany because Europe is opening up to foreign travel faster than the UK.
The airline has switched planes that would have transported British holidaymakers to Europe to Berlin, from where they will fly Germans and other tourists to Spain.
The move will sound further alarm bells in the travel industry that the UK is in danger of losing out to its European counterparts economically as they open up to international travel more quickly.
Most of the main Mediterranean countries, including Spain, Italy, Greece and Portugal, have opened to tourists who can either prove they have been vaccinated, have a negative PCR test or evidence of immunity through having contracted Covid.
The EU has signalled that its green certificate – a single travel document carrying proof – will be operating from July 1, when most of Europe is expected to be open to foreign travel.
The UK, however, remains largely closed with only 11 destinations on its green list from which returning Britons do not have to quarantine.
Only three of these – Gibraltar, Israel and Iceland – are viable holiday destinations, with the most popular Mediterranean countries remaining amber. That status requires a 10-day quarantine on return and at least two PCR tests, on days two and eight.
EasyJet said in a statement: "With 50 per cent of easyJet's flying intra-Europe, we are seeing European governments are progressively opening up using frameworks in place which enable travel and much of it restriction-free.
"And this relaxation and removal of restrictions has sparked a positive booking momentum across Europe, with the majority of our bookings showing a strong swing towards Europe when in normal times it would be a 50/50 split with the UK.
"We are fortunate that we are able to redirect flying on our European network – for example, we have moved capacity from the UK to Palma to Berlin-Palma flying, and over the past week we have added 150,000 further seats to our intra-European network.
"Europe is demonstrating that a safe reopening of travel is possible, and so we continue to urge the UK Government to do so urgently so our customers can reunite with loved ones or travel for a much-needed break."
It comes as it emerged that the Department of Health and Social Care (DHSC) has been forced to set up a specialist complaints unit to provide free NHS Covid tests for hundreds of travellers let down by private firms.
The DHSC operators have told travellers they have been overwhelmed with calls from angry holidaymakers or businesspeople whose tests were not delivered on time or did not turn up.
One Dubai-based British businessman told The Telegraph that he would have had to spend two extra weeks in quarantine because of the 14-day delay in his test delivery if he had not been able to use the back-up team.
Another Portuguese-based entrepreneur said he had turned to the NHS after his test had been delayed, with the operator admitting they were dealing with "a lot" of travellers in a similar situation.
The creation of the team, with the email DHSCtesttracecustomerfeedbackteam@nhs.net, comes after the consumer group Which has warned that the system was at risk of collapse as hundreds of travellers were forced to pay for replacement tests or extend their quarantine.
Rory Boland, the Which? travel editor, said: "Too many people have been left at the mercy of rogue operators and, with little oversight or regulation, these problems will continue to persist."
It came as the Republic of Ireland announced that it was extending the self-isolation period for arrivals from the UK from five to 10 days amid concerns about the Indian or delta variant.
Fully vaccinated passengers can be released from self-isolation on the fifth day if they produce a negative PCR test, Micheal Martin, the taoiseach, said.