The tunnel will be constructed using a total of four TBM’s in two phases – known as ‘Northolt Tunnel West’ and ‘Northolt Tunnel East’.

Two TBMs, named Sushila and Caroline, are already constructing the longer 5-mile eastward Northolt Tunnel section between West Ruislip and Greenford.

The latest TBM to be launched, Emily, will bore a shorter 3.4 miles stretch to later meet these two TBMs at Greenford.

Emily will be joined next month with the launch also from the Victoria Road Crossover Box of the last remaining TBM, Anne, for this shorter stretch of the Northolt tunnel.

Ariel view of TBMs Emily and Anne ready to bore from the Victoria Road Crossover Box

SCS said the quartet of TBMs are all set to complete their journeys on schedule in 2025, when they will be extracted from the ground through giant ventilation shafts at Greenpark Way.

Malcolm Codling, project client director at HS2 said: “We are working at peak construction on HS2, delivering the tunnels which HS2 trains will travel through under London.

“The preparation to launch TBM Emily has been complex and we remain on schedule to complete the Northolt Tunnel in 2025.”

The last section of London tunnelling from Old Oak Common to Euston is presently on hold as the Government reviews delivery arrangements.

Following the decision to axe phase two of the HS2 route to Manchester, The Government said it would deliver this final drive using private sector funding, derived from the redevelopment of the wider Euston London Terminus.

HS2 said it would continue to progress with the present final tunnel drive plan, delivering the two last two TBMs to Old Oak Common station box later this year.

These will be placed into the underground box to await a Government decision on when to begin boring the final Euston Tunnel stretch.