The first of two tunnelling machines has begun excavation works between Old Oak Common and Euston Station as part of HS2’s final 4.5-mile stretch into central London.

The works mark a major milestone for the project after rumours swirled in recent years that HS2 would only reach Old Oak Common in west London due to the high cost of building the remaining few miles to Euston.

Some estimates suggested that by not extending into central London, the overall economic benefits of HS2 could be halved in the long run.

The Department for Transport (DfT) said that taking HS2 all the way to Euston was “essential to unlocking the project’s full economic potential” and was part of wider progress on the project, which included 23 miles of tunnels, 19 bridges and two viaducts along the rail line’s route from central London to Birmingham.

The tunnelling process is expected to take between 12 to 18 months overall, although exact details about the terminus, upgrades to Euston Station and how it will all be funded have still not been revealed.

Rail minister Lord Peter Hendy said he expected that Euston will ultimately end up with more than the six platforms dedicated to high-speed rail that have been previously announced in order to allow for future extensions to the line beyond Birmingham.

The boring machine works by both excavating and constructing the tunnel as it goes, slotting concrete segments into place to build the structure through which HS2’s trains will travel. It is the first of two tunnel boring machines that will construct the two parallel tunnels to Euston and is named ‘Madeleine’ after the former president of the Women’s Engineering Society Madeleine Nobbs.

“It was brilliant to switch on the tunnel boring machine at Old Oak Common today – not just because it’s an engineering marvel, but because it brings HS2’s journey to Euston another step closer to reality,” Hendy said.

“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.”

With over 33,000 people currently working to build the high-speed railway, DfT said the works could provide a £10bn economic boost to the west London economy over the next decade, including 22,000 more homes and almost 19,000 new jobs. 

The delivery of the government’s plans for Euston will be taken forward by a new body, the Euston Delivery Company. Once established, the company will take the lead on the new transport hub, which includes the HS2 station, the redevelopment of the existing station and upgrades to the London Underground station.

Last summer, transport secretary Heidi Alexander told the Commons that HS2 will likely face further delays beyond its expected 2033 completion date because of a “litany of failure”.