London Marathon organisers are considering holding the event over two days instead of one from next year.
It would allow the elite men's and women's races to happen on separate days, while also supercharging the charity money raised by doubling the number of amateurs.
Demand massively exceeds supply every year, with the public ballot and charity places filling up quickly.
Some 56,640 people finished last year's event, a world record according to organisers, and a new high of £87.3m was raised.
The 2027 race would take place on the Saturday as well as the traditional Sunday slot, meaning extended road closures on the famous course that starts in Greenwich and finishes near Buckingham Palace.
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A London Marathon Events spokesperson said: "The TCS London Marathon is the world's most popular marathon, and we are continually exploring innovative ways to enable more people to take part, while delivering positive benefits for London.
"Together with our partners and stakeholders, we are looking at the intention for the 2027 TCS London Marathon to take place across two days.
"No approval has been given at this stage. Our immediate focus is on delivering an incredible 2026 TCS London Marathon on Sunday, 26 April, and ensuring every participant has an amazing experience.
The London Marathon began in 1981 and has raised £1.4bn for good causes in the decades since.
Attracting the world's elite runners, it's one of the seven major marathons alongside New York, Boston, Chicago, Berlin, Sydney and Tokyo.
(c) Sky News 2026: London Marathon could be extended to two days in 2027
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