HS2 has officially begun excavation of the final tunnel bore on the 140‑mile high‑speed railway between central London and the West Midlands — a major milestone for the UK’s largest infrastructure project.
The last of HS2’s 11 tunnel boring machines (TBMs) has started its underground journey from Old Oak Common in west London towards Euston, the line’s future London terminus. The machine, named Karen after pioneering train driver Karen Harrison, marks the final phase of the twin‑bore Euston Tunnel.
To commemorate the launch, two Avanti West Coast train drivers — Hayleigh Richardson and Vicky Knight — joined engineers aboard TBM Karen to assist with the first moments of its drive.
This milestone follows the January launch of TBM Madeline, the first machine excavating the parallel bore of the 4.5‑mile tunnel. Once complete, the Euston Tunnel will allow Britain’s new fleet of high‑speed trains to run directly into central London, boosting capacity, performance and reliability across the national network.
The government has reaffirmed its commitment to a new HS2 station at Euston — a development expected to drive regeneration, unlock homes, and create long‑term employment opportunities.
The launch also comes as HS2 undergoes a comprehensive programme reset led by Chief Executive Mark Wild, focused on project sequencing, efficiency and cost certainty.
Government and Industry Leaders Welcome the Milestone
Rail Minister Lord Hendy said:
“Today’s launch brings HS2’s journey to Euston another step closer to reality, as this Government presses on to deliver this project and with the transformational Euston station redevelopment.
“We’re putting HS2 back on track, and taking the railway into central London is crucial to unlocking its full potential to deliver more jobs, more homes and a long-term boost to the whole British economy.”
Alan Morris, HS2 Ltd’s Line of Route Delivery Director, added:
“The launch of the final HS2 TBM towards Euston is significant milestone in our extensive tunnelling programme. TBM Karen will complete the second bore of the Euston Tunnel, bringing high speed train services directly in and out of the centre of the capital, enabling future economic growth and regeneration.
“While we have been working hard to reset the project, our expert teams have been focused on safely driving up productivity - and today’s final TBM launch is real evidence of that paying off.”
A Tribute to a Rail Pioneer
TBM Karen continues the long‑standing tunnelling tradition of naming machines after women. In recognition of Karen Harrison — one of the first female train drivers in the UK — Avanti West Coast drivers Richardson and Knight were invited to operate the machine at its launch.
Hayleigh said:
“It is a fantastic privilege to be part of this latest milestone for HS2 – it’s not every day you get to swap a train cab for the controls of a tunnelling machine.
“For it to be named Karen is a wonderful tribute to a pioneering woman who helped pave the way for female drivers today.”
Vicky said:
“Karen Harrison’s story is one to admire, and it is great she is getting the recognition she deserves for the influential role she played in shaping our industry.
“I’m honoured to take part in this event to celebrate her legacy, as well as mark another key moment in building the railway of the future.”
Engineering the Final Stretch of London’s HS2 Tunnel System
This final TBM launch completes the suite of machines required to bore all HS2 tunnels connecting London with the West Midlands. Four major tunnels — Northolt, Chiltern, Long Itchington Wood and Bromford — are already complete.
Constructed by the Skanska Costain STRABAG (SCS) joint venture, the Euston Tunnel is HS2’s second deep bore beneath London, following the Northolt Tunnel.
TBM Karen, built by Herrenknecht AG in Germany, was shipped to the UK and reassembled in the Old Oak Common underground station box, 23 metres below ground. The machine stretches 198 metres and operates continuously, excavating spoil while installing concrete segments to form the permanent tunnel lining.
Across both bores, the project will install 48,294 concrete tunnel segments and remove 1.5 million tonnes of spoil, much of which will be transported by rail for reuse in construction projects in Kent, Cambridgeshire and Warwickshire — eliminating over 135,000 lorry journeys.
Jonathan Morris, Managing Director of SCS JV, said:
“We are proud to launch HS2’s final tunnel boring machine, a major milestone for both SCS JV and the wider project as we excavate the twin-bore tunnel towards Euston. During this work the TBMs will remove over 1.5 million tonnes of excavated material and construct the final section of the tunnels using more than 8,000 pre-cast rings.
“Our teams have already delivered 8.4 miles of tunnels under London and will now continue working around the clock to complete these final drives. Achieving this safely and productively is our top priority, with our TBMs progressing at an average rate of around 16 metres per day while maintaining the highest levels of safety performance.”
The tunnel will reach depths of 66 metres, and upon completion, the TBM’s cutterhead will be removed at Euston while its shield will be grouted in place — a common engineering process in deep tunnelling.
TBM Karen’s route will even pass beneath the resting place of legendary engineer Isambard Kingdom Brunel in Kensal Green Cemetery — a symbolic nod to the engineering heritage HS2 aims to build upon.
Image credits: HS2
