British Airways' parent company is mulling legal action over the UK government's planned 14-day quarantine on international air passengers, its boss revealed on Friday.

Willie Walsh, chief executive of airline conglomerate IAG, told Sky News the quarantine, which comes into force on Monday and aims to prevent a second wave of coronavirus, was "irrational" and "disproportionate" at a time when most flights remain grounded.

Irish no-frills rival carrier Ryanair added separately that it would join any legal action against the quarantine. "We think it's irrational, we think it's disproportionate, and we are giving consideration to a legal challenge to this legislation," Walsh said on Friday.

Under the quarantine plan announced last month to try to limit the spread of COVID-19, international arrivals from Monday will be required to self-isolate for a fortnight. Yet it has provoked anger in a sector that is already reeling from collapsing air travel demand.

"We're reviewing that with the lawyers later on today," Walsh said, noting that the proposed quarantine had "torpedoed" IAG's hopes to return to the skies in July. "I suspect there are other airlines who are doing so because it's important to point out there was no consultation with the industry prior to enacting this legislation," he said.

Dublin-based rival Ryanair swiftly welcomed IAG's stance and threw its weight behind any legal move. "Ryanair will support any legal action launched by IAG against this ineffective quarantine," the carrier said in a brief statement.

In a sign of increasing tensions with the UK government, BA snubbed an industry meeting about the quarantine with Home Secretary Priti Patel on Thursday.