The aviation industry has criticised plans for a 14-day quarantine for people arriving in the UK from overseas.
But it comes as many airlines were preparing to resume flights on a smaller scale after weeks of being grounded by virus-related travel restrictions.
Ryanair said it will go ahead with plans to run 40% of flights in July, but its chief executive Michael O’Leary dismissed the quarantine plan as “bonkers”.
He told Sky’s Ian King Live: “You cannot implement an effective quarantine on inbound arrivals into the UK when passengers arriving at airports like Heathrow or Gatwick, [then] get on the London Underground and Gatwick Express to travel into London.
“Every passenger arriving at every UK airport uses buses, trains, public transport to travel to their destination and the government idea that you should only isolate them after they’ve all used public transport shows how ineffective a quarantine is.
“In the UK they’re not applying effective measures, which is face masks, instead preferring to come up with frankly ineffective and bonkers ideas like quarantines.”
The quarantine will mean arrivals having to tell authorities where they will isolate themselves for 14 days – and they could be fined £1,000 if they break the rules.
Road hauliers, NHS workers and people from the Republic of Ireland are exempt.
The rules are not as tough as in some countries, such as Australia and New Zealand, where arrivals are taken to hotels for 14 days in isolation.
Many countries have also banned arrivals who are not citizens or residents.
Heathrow’s chief executive John Holland-Kaye said the plan would “kill off aviation as long as it is in place”.
He told Sky News: “As long as the quarantine is in place then nobody is going to be flying any more than we have today, which is only about 5,000 passengers daily, when normally we would expect at this time of year nearly a quarter of a million passengers.
“If this is what the government needs to do to keep people safe and avoid another outbreak of the disease, then I think we have to support that.
“But we have to have a plan for what happens next so that we can look ahead to how we’d reopen borders.”
Mr Holland-Kaye added: “Aviation is the lifeblood of the UK economy. All those manufacturers who want to get up and running will rely on the supply chain we’re bringing in as well as the exports we take all over the world.
“Equally we have a tourism industry in the UK that relies on tourists coming into the UK and unless we can get those people flying in from safe countries, we can’t get the hotels and the restaurants and so on re-started.
“We risk having, without a plan, a very extended period without flying and we risk having a health crisis becoming an unemployment crisis.”
Mr Holland-Kaye said the government should establish a common international standard for health and aviation with the European Union and the US to “protect jobs in the UK and also perhaps save some summer holidays”.
He added that countries such as Australia, with very low levels of virus transmission, should be among those “we should be opening up to”.
Virgin Atlantic, which is cutting 3,000 jobs due to the pandemic, said the quarantine would prevent it from resuming flights until at least August.
A spokesman said: “We know that as the COVID-19 crisis subsides, air travel will be a vital enabler of the UK’s economic recovery.
“Therefore, we are calling for a multi-layered approach of carefully targeted public health and screening measures, which will allow for a successful and safe restart of international air travel for passengers and businesses.”
Airlines UK, the trade body for UK-registered airlines, said introducing a quarantine at this stage “makes no sense and will mean very limited international aviation at best”.
“It is just about the worst thing government could do if their aim is to restart the economy,” it added.
The government will be reviewing the measures every three weeks, and the trade body has said it must be “robust, transparent and evidence-led, with advice published in full”.