Prime Minister David Cameron (fourth left) and London Mayor Boris Johnson (third right) visit a Crossrail construction site beneath Tottenham Court Road in central London yesterday.

Crossrail, the largest infrastructure project in Europe, which will provide a new link across London, has reached the half-way stage, the company behind it said at a high-profile event attended by Prime Minister David Cameron. The £15bn project, due to open in 2018, will connect Heathrow airport west of London to the county of Essex in the east through 42km of new tunnels in a bid to speed up connections and relieve pressure on London’s crowded underground.

The project is running on time and on budget, confirmed Crossrail yesterday, as it hosted Cameron and London Mayor Boris Johnson at its Tottenham Court Road site in central London, 25 metres underground.

“There was a time when some said that building a huge tunnel deep below the streets of London was a mad plan that would do nothing for our economy. But as this awe-inspiring project hits its halfway point we can see how wrong the naysayers were,” Johnson said.

“Big infrastructure projects like this are vital for the economy of London and the rest of Britain,” said  Cameron. “They are the foundation stone on which business can grow. As we look across London’s famous skyline — from the reconstruction of Battersea Power Station to the upcoming renovation of the Royal Albert Docks — we can see new life being breathed into the city. London, like the rest of Britain, is starting to rise.”

“Crossrail will revolutionise east-west transit in the capital, making London an even more attractive place to visit and invest.” With the city’s population set to hit 10mn by 2030, extra capacity is vital, said London Transport commissioner Sir Peter Hendy.

Crossrail will add 10% more capacity to London’s rail network and help cope with the city’s forecast population growth to 10mn people in 2030 from 8.4mn now, Cameron said.

Around 10,000 people currently work on Crossrail and the project is supporting 55,000 jobs around the country during its construction.

Work began in 2009 and digging the new tunnels has uncovered a range of archaeological finds including 20 Roman skulls and a graveyard which could hold the remains of some 50,000 people killed by the plague more than 650 years ago.

Crossrail is a subsidiary company of Transport for London (TfL), a public authority partly funded by the government’s department for transport.