HS2 MINISTER Huw Merriman today (16) became the first person to officially walk on top of the UK’s longest railway bridge, which is under construction at an HS2 site in the Colne Valley.

The first 480m of the Colne Valley Viaduct – which will eventually stretch for more than two miles across a series of lakes and waterways outside Hillingdon – has been built over the last seven months using a 700-ton ‘bridge-building machine’.

HS2 aims to improve rail links between London, Birmingham and the North.

Mr Merriman said: “This is an extraordinary feat of engineering and architecture, designed to enable spectacular views across a beautiful part of our British countryside which is being preserved and protected by this project.

“It was incredible to be the first person to officially walk on top of it today – another milestone for this monumental project which will transform journeys for people up and down the country.”

Known as a ‘launching girder’, the 160m-long bridge-building machine is used to lift the giant concrete deck segments that form the viaduct’s arches into position. Once each section is complete, the machine inches itself forward to build the next stage.

The first 141 - out of a thousand - deck segments are now in position, with each one weighing up to 140 tons.

To allow for the gentle curves of the viaduct as it crosses the valley, all the segments are slightly different shapes

Once construction is complete, the factory and surrounding buildings will be removed and the whole area between the viaduct and the Chiltern tunnel will be transformed into an area of chalk grassland and woodland.

The design of the viaduct was inspired by the flight of a stone skipping across the water, with a series of elegant spans, carrying the railway above lakes, the River Colne and Grand Union Canal.