MEGA-marathon man Mark Allison says he expects running across Australia to be his toughest challenge yet.

The computer software developer shot to fame running 3,100 miles across the US in 2011, earning him the nickname Run Geordie Run.

Four years earlier, he had run the length of Britain, from John O’Groats to Lands End.

Today (Tuesday, October 8), he flew out of Newcastle Airport bound for Perth – and an awe-inspiring 2,600-mile cross-country run to Sydney.

The 42-year-old will cover up to 41 miles a day for 70 days through desert, plain and Australian Outback, crossing three time zones and braving some of the most extreme conditions known to man.

Having already raised £170,000 for charity, the father-of-one hopes his exertions Down Under will generate £50,000 for the Children’s Foundation and the Sir Bobby Robson Foundation, the late football manager’s cancer charity.

Speaking before he jetted off today, Mr Allison said: “This is the third major charity challenge I have set myself and it will be more gruelling and tougher than ever before.

“I announced that I would be undertaking this challenge nearly two years ago and I can’t believe that it’s almost time for me to make the journey to Perth to get started.

“There are going to be a whole host of daily challenges, the main issue being the extreme daily distances and temperatures to cope with.

“This challenge has been even harder to plan than my previous run due to the remoteness of the locations I will be running through at points.”

The Newcastle United fan, previously of Shotley Bridge, County Durham, and now living in Blyth, Northumberland, will start his run at Cottesloe Beach, Perth, Western Australia, at midnight UK time on Wednesday, October 16.

He hopes to complete the run at the world-renowned Bondi Beach on Christmas Eve.

Run Geordie Run Down Under is sponsored by Sport Newcastle, Chapman Ventilation, Cherry Active, Benfield, Identicom and Virgin Money.

To keep up to date with Mr Allison’s progress or to sponsor him, visit rungeordierun.com, facebook.com/rungeordierun or twitter.com/rungeordierun