Hadleigh’S Olympic mountain biking course is set to be the most challenging in the history of the games, according to Essex’s Olympics chief.

Hidden in a large natural hollow between Hadleigh Castle and the bottom of Chapel Lane, construction is under way on the 5km track.

Access to the site is strictly off limits, due to the heavy machinery being used to build it, but Stephen Castle, Essex county councillor for the Olympics, gave the Echo a sneak preview.

Up close, the steepness of the course becomes alarmingly apparent.

Riders will hurtle along it during the 2012 Games, descending 84m from the course’s highest point to its lowest, while tackling jumps, rocks and U-turns as they go.

For Mr Castle, its difficulty level is a source of great pride, especially as the location was first criticised by those who thought the steep mountains of Wales and Scotland would have been more appropriate.

Mr Castle said: “They think it’s going to be one of the most challenging, if not the most challenging course there has ever been at the Olympics.

“Our track is 84m in height. The course at Beijing was around 50m and even Sydney was only 80m.

“People didn’t think you could build this sort of course in a flat county like Essex. I think they are going to be pretty impressed with the results.”

Mountain biking is one of the youngest Olympic events and was first introduced in the 1996 Atlanta Games.

Most of the track is no wider than 1.5m, but amazingly the riders are able to overtake while hurtling over jumps and around banked bends.

Barbara Mills, delivery manager for the course, said it has been designed to test the world’s best mountain bikers.

She added: “While other Games have adapted existing courses, this one has been built especially for elite standard.”

As well as its height, the track will feature obstacles, such as rocky jumps, also known as drop-offs.

The course designers are still deliberating over the height of the tallest jumps, strikeing a balance between height and what is physically possible. The riders will snake round hairpin bends, many of which are built at the steepest points of the track.

Mr Castle said: “Clearly this is a course that has been designed for Olympic athletes.

“It’s not finished and, on that basis, it would be extremely dangerous for any rider, no matter how good, to try and have a go on it. There is also the possibility they would damage the course.

“Once the Olympics is over, there will be a legacy course for everyone to enjoy.”