A fitness instructor has stepped into the running shoes of his best mate whose son has a rare eye cancer.

Billy French, 29, from Mitcham, is running the marathon on behalf of his Epsom friend Mark Stevens after his son Jack, now 2, was diagnosed last year.

Mr French has already raised more than £1,000 for the Childhood Eye Cancer Trust since replacing Mr Stevens who cannot run in the marathon on Sunday, April 21.

Jack was only found to have a childhood cancer, called retinoblastoma, after his grandmother read an article saying the disease can be seen as a glow in the eye in photos.

Mr French, who lives in Steers Mead, Mitcham, said: "If she hadn't seen that article then nobody would have noticed it.

That's why it is so important to raise awareness of not only the disease but the symptoms too."

Jack, who lives with his family in Chapel Grove, Epsom, is now in a stable condition but has to undergo examinations under anaesthetic every few months.

Less than 50 children a year are diagnosed with retinoblastoma in the UK and many children lose an eye to the disease.

Mr French said it was impossible for children to understand why they cannot eat or drink for hours before an anaesthetic to check their eyes.

He said: "The whole experience is emotional torture. It is just an awful experience for them and everyone involved."

The Childhood Eye Cancer Trust offers support to Jack’s family and others, raises awareness of the disease and helps to fund research.

To donate visit: www.justgiving.com/Billyjackmarathon

For more information visit: www.chect.org.uk