London Marathon runners told to reconsider fancy dress as weather forecast suggests 2018 could be hottest race ever

'Plan to run at a slower pace', add organisers

London Marathon runners have been warned to abandon personal best times and reconsider plans to wear fancy dress due to the hot and humid weather which has been forecast.

Temperatures up to a race-record 23C and high humidity could cause problems for runners, organisers warned as they promised to provide extra water.

Dozens of competitors are thought to be planning an attempt on Guinness World Records while dressed in outfits like a suit of armour, a Paddington Bear costume and ski boots.

Marathon event director Hugh Brasher said: “Most importantly, runners should adjust their goal for Sunday and plan to run at a slower pace. If they were planning to run in fancy dress, they should think carefully if that is appropriate in the forecast conditions.

“We want to stress that there will be plenty of water available and runners should drink according to their thirst and use spare water to douse their head and neck.”

Water will be available every mile from miles three to 25, while runners can pass through six shower stations to cool down at miles nine, 13, 17, 20 and 22.

There will be 39 first aid stations dotted along the route that runners should visit if they feel overly tired or unwell, organisers said.

Met Office meteorologist John West said that while temperatures could hit 23C there was also the potential for “some showers coming in from the west which could take a degree or so off”.

He added: “Showers could be a bit of a double-edged sword because it could make it that little bit more humid for runners.”

Adam Smith, 45, a lawyer, is attempting the record for fastest race dressed as a mythical creature. He said he thought “there won’t be a lot of people doing personal bests”.

He added: “My costume is particularly warm, with a nice and furry gnome hat and a toadstool to carry. The plan is to go on as normal but I’ve asked if I can have short sleeves – I’m very conscious that there’s a world record and then there’s being safe.”

Forecasts for high temperatures on Sunday ranged from 19C to 23C, while the Met Office’s website suggested humidity could hit 71 per cent at 10am, when the mass race is due to begin.

The organisation also warned of a high pollen count on the day, but a low level of air pollution.

The hottest London marathon on record was 22.7C in 1996, the Met Office said.

Warnings to runners came as Britain enjoyed its hottest April day since 1949, with the mercury hitting 29.1C in St James’ Park, central London, on Thursday.

Additional reporting by agencies