During April 2020, it was announced that a contract worth approximately £3.3 billion had been awarded to a joint venture company, Skanska Costain Strabag, for the tunnel's construction.

[2] At the time, HS2 Ltd, the delivery company behind the line, stated that the use of a tunnel was the optimum solution, reducing the disruption caused by the railway's construction upon the local community while also accelerating the timetable for that portion of the route.

[5] During early 2018, a layer of black clay was discovered, which has been dubbed the "Ruislip Bed"; this material dates back 56 million years and was formed from densely wooded marshes at the coast of a sub-tropical sea.

However, this option was formally dismissed in a report released in February 2015, primarily due to the increased costs and construction time that such a change would predicted to involve.

The first two TBMs, with a cutter-head diameter of 9.82 m (32.2 ft), are designed to bore through Lambeth Group rock, chalk and London Clay, and will assemble 4,220 tunnel segment rings each.