However, Tuesday’s strike (6 August) remains on and will go ahead as planned if the airport and the union fail to reach terms over a new pay deal on Monday.

Heathrow pre-emptively cancelled around 15% of its Monday flight schedule in anticipation of the strike, with some airlines since confirming these flights will now go ahead.

Air Canada has said it will operate its full flight schedule, while Aer Lingus, Etihad and Portugal’s TAP Air have confirmed they will aim to reinstate flights.

Virgin Atlantic opted to relocate its Heathrow flights to Gatwick and has confirmed these will not now revert back to Heathrow.

Around 4,000 Unite members – including security personnel, firefighters, engineers and passenger service operators – are expected to take part in any action, should the strikes go ahead.

Beyond Tuesday’s walkout, Unite has strike action planned over 23-24 August.

A further two groups of Heathrow workers last week voted in favour of joining the strikes, mainly comprising engineers, airside operation controllers, airfield transport officers and environmental officers.

Unite says the dispute centres around pay disparities between workers doing the same job and what it feels to be the disproportionate remuneration for Heathrow’s senior executives.

Monday’s talks will take place under the auspices of government conciliation service Acas. The union said it would make no further comment while the talks are ongoing.

A Heathrow spokesperson said: “We will continue talks with Unite tomorrow and we remain hopeful we can find a resolution and stop this disruptive and unnecessary threat of strike action.

“We recommend passengers check their flight status before travelling to the airport and read the guidance on heathrow.com to prepare for their journey.”