The largest-ever field of runners are facing soaring temperatures as they pound the streets in this year's London Marathon.

The 36,500 athletes are making their way around the famous 26.2 mile course in sunny weather which is expected to reach highs of 23C. Extra doctors, vast supplies of water and special showers are on hand to help them deal with the heat.

Many of those taking part in the marathon, which passes famous London landmarks such as the Cutty Sark, Tower Bridge, Big Ben and the Houses of Parliament, before finishing in The Mall, will be running for charity.

Among them is Wandsworth Guardian reporter Alexander Carnwath who is raising money for Hemihelp, a charity which supports children with hemiplegia, a condition similar to cerebral palsy which affects one side of the body.

Also hoping to complete his first marathon is Guardian graphic designer Bob Noble. After being plagued with injuries in the run up to the big day, Bob is hopeful his Achilles tendon lasts the course.

Others running the race include the original drummer and spoon player with 1960s group The Bonzo Dog Doo-Dah Band.

Battersea's Martin Ash, 65, whose stage name is Sam Spoons, decided to take up the challenge after returning from the band's recent reunion tour. He hopes to raise £4,000 for Age Concern.

Celebrities taking part include EastEnders star Kara Tointon, model Nell McAndrew, Matt Dawson, Olympic hurdle champion Sally Gunnell and wheelchair basketball player Ade Adepitan.

Organisers said the best medical attention is available to deal with any casualties in the high temperatures.

London Marathon chief executive Nick Bitel said: "It's sensible for the runners to look at the weather conditions and adjust their own goals."

Mr Bitel said: "We're putting out over 1,300 first aid volunteers from St John Ambulance, over 100 doctors on the course, some of the world's leading medical experts are here to help, including from places as far afield as South Africa and America."

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