The ambitious Crossrail project has celebrated reaching its halfway point.

To mark the occasion, officials such as the mayor of London and the prime minister ventured 25 metres underground to see the progress for themselves.

The milestone comes five years after work began on the £14.8 billion project, with engineering and tunnelling work expected to be completed later this year. After that, focus will shift to station construction and development of the railway.

Once complete, Crossrail will add ten per cent to the capital's railway capacity and will serve a total of 38 stations. It is anticipated the project will generate at least 75,000 business opportunities. 

London mayor Boris Johnson said: "Crossrail will revolutionise east-west transit in the capital, making London an even more attractive place to visit and invest."

The project is just part of Transport for London's ambitions programme of investment, sitting alongside plans to modernise the underground system and the road network. The first Crossrail trains are expected to run through capital in 2018.