Engineers have begun assembling two giant tunnelling machines that will dig the final 4.5 miles of underground high-speed railway to carry HS2 trains into the heart of London.

The work started as Mark Wild joined HS2 as the company’s new chief executive.

The former CEO of Crossrail will help oversee the project’s transition from a major construction programme to a working railway, with a renewed focus on controlling costs.

The green light was given for the HS2 tunnel between Old Oak Common and London Euston in the recent Budget

Weighing 1,250 tonnes, each of the tunnel boring machines (TBMs) will launch from an underground box at one end of the project’s Old Oak Common station.

They are expected to take around one-and-a-half years to reach the railway’s final southern terminus at London Euston.

In keeping with tradition, the TBMs have been given female names after prominent women in history.

One machine is called Karen after Karen Harrison, the first female train driver in the UK who was based out of Old Oak Common depot. The second is named Madeleine, after Madeleine Nobbs, the former president of the Women’s Engineering Society.

The TBMs are the final set to be launched for the railway between London and the West Midlands.

HS2’s London tunnels contractor, Skanksa Costain STRABAG (SCS) joint venture, is leading construction of the twin-bored tunnel. Boring is expected to begin in 2025.

James Richardson, managing director SCS JV, said: “We are delighted that the government has given the green light to delivering HS2 through to Euston, ensuring the full benefits of the new railway are realised.

“Over the past two years, we have continued with critical activities to ensure that we can deliver the Euston Tunnel and approaches quickly, and at the lowest possible cost.

“We are also making excellent progress on the tunnelling between West Ruislip and Old Oak Common, with four TBMs in operation, and the works well over 50% complete.”

Huw Edwards, stations delivery director at HS2, added: “A terminus station for HS2 in the heart of the capital will provide a vital gateway for passengers travelling to and from the Midlands and North, and will undoubtedly lead to the transport-led regeneration of Euston – supporting growth in the local economy and creating thousands of new homes and jobs.”

Final plans for the future HS2 terminus station at Euston are still under review and HS2 is continuing to work with government and other stakeholders to develop an affordable station design that can run HS2 services from London to the Midlands.