British Airways will maintain only limited services if the UK government imposes a 14-day quarantine on arrivals, Willie Walsh, chief executive of BA parent IAG, has warned.

Walsh slammed the idea of using quarantine measures to ease the coronavirus lockdown, saying: “If there is a 14-day quarantine, I would not expect us to be doing any flying, or very little flying.”

The IAG chief said he could not envisage “people will want to fly into the UK if they are forced to quarantine for 14 days”.

Walsh also ruled out leaving middle seats empty on aircraft, saying it was impractical.

Transport secretary Grant Shapps is considering quarantine measures for arrivals once Foreign Office advice against all but essential travel is relaxed.

The quarantine rules would be similar to those already in force in some countries.

Walsh also hit out at the suggestion construction of a third runway at Heathrow would go ahead, suggesting it was now “impossible”.

He said: “There is not going to be a third runway.”

Walsh suggested: “If Heathrow wants to build a third runway they have to acquire the BA headquarters at Waterside. I don’t expect they will be rushing to do a deal.”

Heathrow chief executive John Holland-Kaye told a parliamentary select committee this week: “I’m not thinking about a third runway at the moment. But in 10 or 15 years we will need a third runway.”

The airport this week won the right to appeal to the Supreme Court against a Court of Appeal ruling that the government’s go ahead for a third runway had been unlawful.

Walsh’s insistence that Heathrow would not expand came despite a leaked BA memo suggesting the airline could pull out of Gatwick and consolidate its operations at Heathrow as part of a post-Covid-19 restructuring.

The IAG boss, a long-time supporter of expansion at Heathrow, has been sharply critical of Heathrow Airport’s plans for the third runway on the grounds of its cost.

Speaking as IAG reported a €1.7 billion loss in the first quarter of the year, Walsh warned of further job losses at IAG-owned carriers, including BA, Aer Lingus, Iberia and Vueling, but gave no details.

BA announced plans to cut up to 12,000 jobs, 30% of its workforce, in late April.

He confirmed he was happy for IAG carriers to access government aid in the form of general support schemes, but insisted: “I’m opposed to illegal state aid which typically applies to aid given to a failed company.”

BA has accessed UK government funds under the Coronavirus Job Retention Scheme, and Iberia and Vueling have secured more than €1 billion in state aid in the form of a grant and loan guarantee in Spain.

However, Walsh declined to criticise Virgin Atlantic for seeking £500 million in UK government aid, saying: “I don’t think it [Virgin Atlantic] is a failed company.

“I would not define it as a well-run company because they have not been profitable. [But] with the right management at Virgin and the right focus, it’s a business that could be run profitably.”

Virgin Atlantic is pursuing funds from new investors as well as continuing to negotiate with the government over potential funding. It announced more than 3,000 redundancies and its withdrawal from Gatwick this week.

IAG confirmed on Thursday that Walsh will step down as chief executive on September 24 to be replaced by current Iberia chief executive Luis Gallego.

Walsh had been due to step aside in March and retire in June but agreed to stay on during the Covid-19 lockdown.

IAG chairman Antonio Vazquez said: “We are grateful that Willie delayed his retirement at this challenging time providing the airlines’ management with the necessary stability to focus on the immediate response to the crisis.”