"Does a ginger beard count?" wrote one person, while others debated whether "strawberry blonde" would be accepted.
One such marginal redhead, Luke Young, 31, from Peterborough, told The Washington Post that the idea was "good marketing" even if he wasn't a full redhead but instead only had "a beard the colour of a 'Moroccan sunset'".
"A free ticket is a free ticket," he said.
Millions of people in Britain stayed home or sought shade during the country's first-ever extreme heat warning, as the hot, dry weather that has scorched mainland Europe for the past week moved north, buckling rail lines and forcing two airports to close their runways.
The red heat alert covers a big chunk of England and is to last through Tuesday, when temperatures may reach 40C for the first time, posing a risk of serious illness and even death among healthy people, according to the Met Office, the UK's meteorological agency.
The extreme heat warning stretches from London in the south to Manchester and Leeds in the north.
The temperature Monday reached 38.1C at Downham in eastern England, just shy of the highest-ever recorded in Britain — 38.7C, a record set in 2019. The country isn't at all prepared to handle such heat — most homes, schools and small businesses in Britain don't have air conditioning.
Flights were suspended at London's Luton Airport as engineers repaired the runway "after high surface temperatures caused a small section to lift". RAF Brize Norton, a major air force base northwest of London, also closed its runway because of the heat. The air force said "aircraft are using alternative airfields in line with a long established plan".
Temperatures are expected to rise further as the warm air moves north on Tuesday, Met Office CEO Penelope Endersby said.
"So it's tomorrow that we're really seeing the higher chance of 40 degrees and temperatures above that," Endersby told the BBC. "Forty-one isn't off the cards. We've even got some 43s in the model, but we're hoping it won't be as high as that."
- Additional reporting, AP
