Two brothers will be tackling one of the toughest races on earth to raise money for the charity supporting their blind sister.

Sam and James Stafford Allen, from Castle Acre, near Swaffham, are to compete in the 156-mile Marathon des Stables in April this year.

It will see them endure temperatures of up to 50C over a six-day period across the Sahara desert, all while carrying their own food and equipment.

The pair are taking on the challenge in aid of the charity Sense, which has supported their sister Felicity, 27, for several years.

She suffers from a variety of complex disabilities affecting her mobility and is also blind.

James Allen, a 31-year-old former captain in the grenadier guards, said: 'Our sister has a rare genetic disorder whereby she has slowly lost her ability to carry out every day tasks. And while her disabilities are pretty complex, Senses have always provided good support to her.

'The race is also something we have spoken about for a few years now and we have always wanted to do it.'

They have now set up an online donation page for the Senses charity, and hope to raise £5,000 for the organisation.

Mr Allen, who ran his first marathon while he was at university in 2006, said his 32-year-old brother and himself had been training for the past year for the event.

Last summer they completed - and won - a 43-mile section of the Windsor Ultra race.

And in the coming weeks they will be taking part in the Peddars Way Ultra Marathon, which is around 48-miles long.

But Mr Allen said the Marathon des Stables will be far more challenging than anything they had faced before.

'Rather than being a standard running race, it comes with several other variables,' he said.

'One is that you have to carry all of your kit, all of your food and sleeping stuff. There is the varying terrain, and then there is the temperature.

'We just want to complete it, but we would also like to come in the top third or higher [amongst competitors].'

To sponsor the brothers, visit http://uk.virginmoneygiving.com/StaffordAllenBrothers