Warnings for London Marathon runners amid predictions that Sunday’s race could be the hottest on record.

Said to be the hottest April day in 70 years, April 19 saw temperatures rise to an overwhelming 29C in central London.

Sunday will see temperatures of 23C prompting marathon organisers to add more water, ice and shower stations along the 26.2 mile route.

Conditions may be especially difficult for fancy-dress runners, including the almost 100 attempting Guinness World Records dressed in outfits like a suit of armour, a Paddington Bear costume and ski boots.

Regular runners are being advised to consider dropping their goal-times and run more slowly.

Adam Smith, who is attempting the record for fastest race dressed as a mythical creature, told the Press Association: "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.

The 45-year-old lawyer, who has run eight marathons, is raising money for Muscular Dystrophy UK, having lost three family members to the disease.

The hottest London marathon on record was 22.7C (72.9F) in 1996, the Met Office said.

Marathon event director Hugh Brasher said: "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."

Met Office meteorologist John West said: "Showers could be a bit of a double-edged sword because it could make it that little bit more humid for runners."

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

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