Two north Norfolk women will be taking on the challenge of a lifetime next weekend, when they set off to Lincolnshire to negotiate the world's biggest and toughest obstacle course in aid of a national blood cancer charity.

Close friends Harry Leggett and Laura Mills, of Sheringham, last year teamed up with pals Kate Bywater and Maria Suffolk to raise more than £5,000 by hosting a dinner dance and auction at the Links Hotel, West Runton.

The cash went to the Stroke Association, which Kate was keen to support as she suffered a stroke after giving birth to daughter Lola six years ago, and the Antony Nolan charity, which Harry found out about when, last year, her husband Jon was diagnosed with a rare and aggressive form of leukaemia.

Jon, 36, is now in remission and is back at work as a project manager at Norwich City Football Club but, inspired by the success of their previous fundraising efforts, mum-of-three Harry, 34, and mum-of-four Laura, 36, were keen to take on a new challenge.

They have teamed up with Harry's brother Brad Fisher and nearly twenty members of his gym, Norwich Fitness Club, to sign up for the annual Rat Race Dirty Weekend, a 20-mile, 200-obstacle challenge taking place in the grounds of historic Burghley House, at Stamford, near Peterborough.

'When we first entered, we thought yes, we can do that,' Laura said. 'But I don't think at the time either of us realised just how much training was involved.'

The event, which kicks off on Friday with a world record attempt backwards-running three-legged race, will see up to 8,000 entrants attempt to raise more than £1 million for charity by crawling under nets through mud, jumping from platforms, scaling a wall of tyres, swimming on their backs through a cage and tackling other obstacles including the world's longest monkey bars.

Harry and Laura have already exceeded their target of £500, with Brad, who has planned a string of events, raising £5,000 towards his target of £20,000.

'Because there is a chance Jon's leukaemia could come back, we really want to support Antony Nolan as, if it does, he will need stem cell transplant and they are the ones who will be able to match him up with a donor,' Harry said.

To support the friends visit www.justgiving.com/fundraising/HARRY-LAURA