Joe Topp (13) and George Gilliatt (13), both pupils of The Petersfield School, ran 26 miles along the Thames path in London on Saturday.

They were joined by both of their mothers, Anita Topp and Helen Gilliatt, for the challenge, which acted as a fundraiser for Cancer Research UK.

Joe took on the run after both his grandads fought and recovered from cancer.

His maternal grandfather Frank Hall was struck with prostate cancer before receiving the all clear, while his father's dad Ken Topp had bowel cancer, from which he is now in remission.

The cancer scares inspired Joe to take on the extraordinary challenge of running a full marathon at the age of 13.

The four runners set off from Hampton Court at about 8.10am and arrived at the London Eye six hours later, exhausted but delighted to have made it to the end.

They stopped along the way for short coffee breaks, with Joe and George fed plenty of sweets to ensure they had enough energy to make the finish.

"By the end I was dragging myself," Joe said.

"It went really well but my legs are very sore – they feel like lead now. But we all did it in under six hours."

The weather for the run was perfect, with the shadow of the trees and buildings along the path keeping them shaded from the heat.

However, it was not all plain sailing as they weaved their way through the pedestrians and tourists along the route.

George fell over 10 miles into the run and needed a plaster to patch him up and get going again.

"It was pretty hard," Joe said. "George fell over and needed a comedy plaster but we got through it.

"We were expecting it to be busier than it was to be honest.

"It was pretty quiet until about a mile before the London Eye, that was when it started to get busy."

Joe admitted when he finally caught sight of the London Eye landmark, he felt relieved.

He said: "We were just crossing Westminster Bridge and my mum saw it and she shouted out.

"I caught the London Eye out of the corner of my eye. When I saw it I felt like celebrating."

He added: "I am really pleased with all of us and so happy that we made it."

Joe first came up with the idea for the fundraising run after watching comedian Eddie Izzard's epic 43 marathons in 51 days on Television.

"As soon as I saw that on TV I knew I had no option but to do it," Joe said.

The boys trained for the big day for 12 weeks, running around Queen Elizabeth Country Park for two or three hours at a time.

Joe's mum Anita felt the boys' run was a great achievement for them.

She said: "Beforehand we made sure that the boys had already covered a fair amount of the route.

"I think we did the first third of it running constantly, then after that we kept making them stop to have drinks and sweets.

"They were both absolute superstars and we were really, really proud of them."

The boys were repaid for their strenuous efforts with £280 in donations for the charity so far but they are looking for more donations now they have completed their challenge.

Anyone interested in donating some more funds can log-on to Joe's fundraising page at: www.justgiving.com/joesthamesmarathon