Callum, ten, cycling from Butler's Cross to his granny's home in Sussex after she was diagnosed with rare eye cancer

On Saturday April 13, Callum will set off from his family's home in Butler's Cross, to his grandmother Sue Harris’ home in Angmering in Sussex, near to the South Downs National Park.

His initial target was £50, before his mother Jennie Smith convinced him to up it to £100.

With more than a week until the ride, Callum has blown this figure out of the water, raising £2,285 so far.

Callum, a pupil at Monks Risborough Primary School, said: “I’m just over the moon.

"I can’t believe it.”

When asked why he was doing the bike ride for his grandmother he said: “Because I love her.”

Sue was diagnosed with ocular melanoma in January last year - a condition that affects around 600 people a year in the UK.

Only three centres in the country can treat it - Liverpool, Glasgow, and London.

Callum’s chosen charity is OcuMel UK, which is run by eye cancer patients and their families to support others affected by the illness and to improve treatment.

Callum's mum Jennie said: "It is such an amazing thing for him to do - it is a huge challenge but it would mean a lot to his gran.

"It was quite overwhelming when he first told me he wanted to do this to help his gran and anyone else who suffers from the condition.

"Cycling has always been a love of Callum's - he started at the age of three and we bought him a second hand road bike in January which he loves.

"He has been shocked at people's generosity and I don't think he can comprehend the amount raised so far.

"Callum is determined to finish - we just hope the weather is good over the two days."

Jennie will be accompanying Callum throughout the cycle - the pair plan to cycle to Guildford on Saturday 13 and then after an overnight stop complete the rest of the route to Angmering on Sunday 14.

Sue, 75, who works as a magistrate said she was ‘completely taken aback’ when she heard what her grandson was doing.

She said: “It did reduce me to tears.

"I am very, very proud of him and deeply touched, especially that he is only ten and he thought up the idea himself.”

Sue first noticed a brown spot in her left eye around two years ago and went to get it checked at her local opticians – but the cancer is so rare that it was overlooked initially.

Months later, when it changed shape, she decided to get a second opinion – and was sent to Moorfields Eye Hospital in London where she was diagnosed and treated using a focused form of radiotherapy.

Sue said her cancer was under control, and was not growing – and she was having regular scans in London to make sure it did not spread to her liver, which occurs with ocular melanoma.

To greet her grandson and daughter, Sue will be putting up flags at the finish line.

She said: “The message I want to get out there is that everyone should get an eye test every two years with dilation drops, so these things can be picked up early.”

To donate visit www.justgiving.com/fundraising/callum-smith09