The boss of Heathrow Airport told UK government ministers unless they "get a grip" on delays at the border, planes will be diverted to foreign countries.
John Holland-Kaye said on Thursday he was not confident international travel would resume on May 17, as outlined in Britain's road map out of lockdown, if Border Force staff could not handle the small volume of arrivals at present.
He said on some days there were just two officers checking the documents of passengers, leading to six-hour queues for travellers on arrival.
Consumer advocate Which? said on Thursday the beleaguered Covid-19 testing scheme for quarantining passengers could buckle under the pressure of demand when widespread travel resumes.
Additionally, there is concern that the UK’s National Health Service app will not be updated in time for May 17 after it was identified as the platform that will carry the Covid-19 passport for passengers who have been vaccinated or tested negative for the virus.
Mr Holland-Kaye said a single A380 jet with 500 passengers on board created a one-kilometre queue at the border.
He said planes could be diverted to EU airports, such as Charles de Gaulle Airport in Paris and Frankfurt Airport in Germany, if the situation persisted.
“That is a disaster for anyone travelling and should be an embarrassment for the UK government if this is how we manage our border,” he told Sky News.
“Heathrow and other airports have turned away flights in recent weeks because of congestion in immigration and if they can’t cope at these tiny volumes, how are they going to cope after May 17?”
Heathrow Airport delays 'could hold back economic recovery'
Mr Holland-Kaye said the Home Office – which controls passenger arrivals – had failed to address the problem. He urged officials to fix the issue so it does not become a “stranglehold on the UK economic recovery”.
“They need to stand up and get a grip on this and make sure we give a really warm welcome to all the passengers coming into the UK in a few weeks’ time,” he said.
“We have not seen quite enough action to ensure we are confident that Border Force can cope on May 17.”
Meanwhile, the Home Office told passengers arriving in the UK to expect lengthy queues.
“We are in a global health pandemic, and people should not be travelling unless absolutely necessary,” it said.
"Queues and wait times will be longer if passengers have not completed the necessary requirements to enter the UK. Airlines are responsible for making sure that their passengers have completed all the necessary requirements, and airports have a crucial responsibility for ensuring travellers can social distance at passport control.”
Transport Secretary Grant Shapps told the House of Commons that the e-passenger gates were being converted to recognise Covid-19 documentation but said the new system would not be ready until later in the year.
Heathrow Airport on Thursday announced a first quarter loss of £329 million ($458m), taking losses since the start of the pandemic to nearly £2.4 billion.
It said only 1.7 million passengers travelled through the London airport in the three months to March 31, down 91 per cent compared with the first quarter of 2019.
Heathrow, which recently lost its status as Europe's busiest airport to Charles de Gaulle, said uncertainty over government policy meant its passenger forecast for the year was 13 million to 36 million, compared with 81 million in 2019.
The Times reported on Thursday that the NHS app would be ready "later in the summer" – missing the May 17 deadline.
It is understood ministers and app developers have yet to agree on its functions, although Mr Shapps on Thursday said the app was being transformed for Covid certification.
“In terms of vaccine certification, we are working on an NHS application; it will be the NHS app that is used for people when they book appointments ... to be able to show you’ve had a vaccine or you’ve had testing. I’m working internationally with partners to make sure that system can be internationally recognised, as that’s the way forward,” he said.