There could be a record-breaking number of flights using British skies on one day as English football fans fly to Madrid for the Champions League final.
Around 9,000 flights are predicted on Friday, which would exceed the previous record of 8,854 set on 25 May 2018.
Air traffic controller Nats said there would be a surge in chartered flights and private jets ahead of Saturday’s clash between Tottenham and Liverpool.
Greenpeace said it showed Uefa was not taking climate change seriously.
As they begin their journeys to Madrid, fans have been posting their progress on social media.
With flights to the Spanish capital at a premium, many have had to go via other countries to reach their final destination.
Nats has predicted an extra 800 flights will take off over the weekend, but that could increase as some private jets may not have registered their flight plans yet.
That number is on top of the 8,000 flights it would handle on a typical day at this time of year.
It says more than half of the extra charter flights will be to and from Liverpool Airport.
Among the thousands of fans heading to Madrid is Conservative MP – and Tottenham supporter – Tracey Crouch, who tweeted a picture of her toenails painted with blue sparkles for the occasion.
A Nats spokeswoman said it would be a huge undertaking to look after the extra flights at what is already the busiest time of year.
She said: “There is no doubt this is going to be a challenging weekend, with limited capacity on the ground at some airports and in the air making delays possible.”
Greenpeace said playing the final in Madrid – despite both teams being from England – had the same environmental impact as “producing, driving and disposing of over 1,500 family cars”.
Areeba Hamid, climate campaigner for Greenpeace UK, said: “It’s more than obvious that Uefa is not taking climate change in the least bit seriously. All sectors, including international sports like football, will have to look at reducing their emissions rapidly if we are to halt irreversible climate breakdown.
“The first step towards football doing its bit should be Uefa accepting that we are in a climate emergency, and making their decisions in that context.”
Last Friday 24 May had been forecast to be the busiest day for flights to date – with a bank holiday, school half-term, the Monaco Grand Prix, and Cannes Film Festival contributing to a spike – but it fell just shy of the record with 8,742 flights taking place.
Nats said there was “a good chance” the record would be broken this time, adding that it would be able to confirm the figure by Monday.