From Monday (8 June), UK arrivals will be required to self-isolate for 14 days. The government said the move is an important step in guarding against a second wave of coronavirus infection.

However, IAG chief executive Willie Walsh said the policy had been pushed through without consultation with the sector, and had torpedoed BA’s hopes of resuming flight operations in July.

"We think it’s irrational, we think it’s disproportionate, and we are giving consideration to a legal challenge to this legislation," said Walsh on Friday (5 June).

In a statement, Ryanair said it would “support any legal action launched by IAG against the UK’s ineffective and useless visitor quarantine”.

Meanwhile, Ryanair has urged on Irish taoiseach Leo Varadkar to scrap the country’s quarantine measures after the EU Commission on Friday called on member states to lift all EU border restrictions by the end of June.

The budget carrier, which is headquartered in Dublin, said Ireland’s quarantine was pointless as arrivals would inevitably mix with others on public transport while travelling to their designated quarantine accommodation, and while shopping for essentials while under quarantine.

It also points out the quarantine excludes visitors from the UK, which currently has the highest rate of coronavirus infection in Europe. Ryanair plans to resume flying in earnest on 1 July when it will restore 40% of its normal flight schedule and operate to 90% of its pre-Covid route network.

“If the EU is ready to reopen, why does Ireland insist on adding obstacles with an ineffective and useless visitor quarantine?" said Ryanair chief executive Eddie Wilson.

Wilson said Ryanair would follow European Aviation Safety Agency and European Centre for Disease Prevention and Control protocols when it returns to service, measures he said were based on "expert evidence".

"We call on the Taoiseach to follow the EU advice and agree on a coordinated reopening of Ireland to visitors without any visitor restrictions from the end of June."