HS2: Excavation under way on ventilation shaft for tunnels

The 78m (255ft) deep shaft near Chalfont St Peter will serve two HS2 tunnels

Work has started on the first of five shafts set to serve two 10-mile long tunnels on the HS2 high-speed rail network.

Engineers have begun excavating the 78m (255ft) deep shaft near Chalfont St Peter in Buckinghamshire

Two giant tunnelling machines will construct the tunnels under the Chiltern Hills.

HS2 is a high-speed rail line planned to link London with Birmingham and on to Manchester and Leeds.

The shaft is one of the five which will be built in the area

The shaft will reach down to the twin tunnels, using fans to regulate air quality and temperature.

• Hundreds of jobs promised in £570m HS2 build

• HS2 to move 3,000 bodies from medieval churchyard

• 'Once-in-a-lifetime' find of rare Iron Age coins

It will also be able to remove smoke in the event of an emergency and provide access for emergency services.

It is expected the tunnels will take three years to complete.

Providing ventilation and emergency access, the shaft will be topped by a barn-like building which HS2 says will be sympathetic to the surrounding environment

A 120-tonne drilling rig with a specialised cutting head was used to excavate the walls of the shaft

The 78m (255ft) deep shaft near Chalfont St Peter will serve two HS2 tunnels