The A3 Hindhead tunnel under the Surrey Hills will be 1.25 miles long.

The longest land road tunnel in the UK is a step closer to completion as excavations from the north and south met in the middle yesterday, deep beneath the Surrey Hills near Hindhead.

Construction company Balfour Beatty is working on the £371 million project to create a tunnel that will carry traffic on the A3, running between London and Portsmouth, which would otherwise have threaded its way up the Devil’s Punch Bowl and through the town.

The scheme will divert a length of 6.7km (some 4 miles) of the existing A3 Portsmouth Road on to a new alignment, with a 1.8km section (about 1.25 miles) that passes under the Devil’s Punch Bowl, placed in a twin bored tunnel, associated side roads and private means of access alterations, and the detrunking of a superseded section of the existing A3.

In an area of Outstanding Natural Beauty, the tunnel will reduce the traffic at what is a notorious bottleneck, and restore peace and tranquility.

Transport Minister Paul Clark said: “Today’s breakthrough is a major step forward for this important Highways Agency scheme. It will bring faster and safer journeys on the only trunk road between Portsmouth and London – as well as freeing the centre of Hindhead from the daily gridlock that blights the area.

“This will deliver real benefits to local people, whether they are drivers, horse riders, cyclists or pedestrians, whilst creating a better habitat for local wildlife and preserving the beauty of the landscape.”

Further to the 30,000 vehicles taken away from the Surrey Hills, the tunnel will also improve the amenities available to local communities. Several underpasses will be created to allow horse riders, cyclists and pedestrians to cross the A3 in safety, alongside a 9km cycle route.

With the completion of the tunnel and approach roads remaining, the scheme is due to open to traffic in summer 2011.