WORK on the UK’s longest railway bridge ramped up this week as HS2 began production of 1,000 huge concrete segments that will form the deck of the Colne Valley Viaduct.

Stretching for 2.1 miles across a series of lakes and waterways on the Hillingdon and Hertfordshire border, the viaduct will carry high-speed trains between London, Birmingham and the North.

The huge deck segments – which weigh up to 140 tons – are being made on site at a temporary factory built specifically for the project.

The mammoth building, which is visible from the M25, has an internal space larger than the Royal Albert Hall.

HS2 Project Client David Emms said: “We’re already making strong progress on the Colne Valley Viaduct – sinking the foundations, building the first piers, and now starting production at the new modular viaduct factory.

“Once complete, this iconic structure will carry trains at up to 200mph. It’s great to see how much progress has been made.”

Every segment will be a slightly different shape depending on where it fits into the viaduct and the on-site factory avoids bringing them in by road.

The factory and surrounding buildings will eventually be removed and the area between the viaduct and the Chiltern tunnel transformed into chalk grassland and woodland.