There are still considerable risks in delivering a multi-billion cross-London railway programme by its target time of 2019, an influential group of MPs have concluded.
The Public Accounts Committee (PAC) warned the £15.8 billion Crossrail project had been undersold by the Department for Transport (DfT).
As a result, the DfT had mixed success securing contributions from businesses and Heathrow Airport Ltd would now only provide £70 million - less than a third of the funding originally agreed.
Costing £14.8 billion, with the trains costing a further £1 billion, Crossrail will stretch from Reading in Berkshire to the west as far east as Shenfield in Essex and will transform cross-London train journeys.
However, PAC praised the project for being "broadly on schedule and delivered within budget"
The Thames Tunnel, a nearly two-mile railway line that will help connect Reading in Berkshire to Shenfield in Essex as part of the Crossrail project, will be unveiled by the Chancellor today.
Part of the £14.8 billion Crossrail project, it is expected to cut journey times and boost rail capacity in London.
George Osborne said the project will provide a major boost the economy.
"As part of our long term economic plan we are investing in infrastructure around the country to create a more balanced, resilient economy," he said.
"Crossrail is not only providing extra speed and capacity for London's passengers, but also supporting new housing, jobs and businesses."
The project is expected to generate 75,000 business opportunities and support the equivalent of 55,000 full time jobs across the UK, according to the Government.
George Osborne has said Derby-based Bombardier's contract to supply Crossrail trains is "great news for British manufacturing, and a real boost for the British economy".
The Chancellor claimed the £1 billion deal was also a "vote of confidence" in the Government's economic plan.
There have been so many twists and turns in the crossrail bidding process, Hollywood should take an interest.
The Derby firm at times looked like the underdog, overshadowed by the giant, Siemens. The Germans delivered a painful blow to the midlands team when they got the massive Thameslink contract.
Then in a moment of corporate high drama Siemens pulled out of the race for the new London contract at Crossrail.
The result brings job security to Derby - and far beyond as Bombardier's long supply line also benefits.
Winning the £1 billion contract to supply the Crossrail trains is a "huge boost" for the company, Bombardier's managing director has said.
Francis Paonessa said the Derby company had spent £20 million developing the Aventra train which will be built for the route.
He added that when built the train will be painted purple and black.
Prime Minister David Cameron has congratulated Derby-based Bombardier on securing a £1 billion contract to supply the trains for the cross-London Crossrail project.
The decision to award Derby-based Bombardier with a £1 billion Crossrail contact is a "fantastic and deserved result", the Rail, Maritime and Transport union general secretary has said.
Bob Crow says the win will "go a long way to saving the future of train building in the nation that gave the railways to the world".
Business Secretary Vince Cable said the decision "represents a real vote of confidence in British manufacturing, supporting 760 UK manufacturing jobs and 80 apprenticeships".
More than 240 jobs will be created and hundreds more secured as a result of the government's decision to award a £1 billion contract to Derby-based trainmaker Bombardier.
Transport chiefs have also revealed they expect the deal to boost the British economy as a whole, with around 74 per cent of the supply chain spending to remain in the UK.
The deal, announced this morning by Transport for London and the Department for Transport, will secure the future of 760 jobs at the plant in Old Oak Common, plus 80 apprenticeships.
It will also mean 244 new jobs will be created, along with 16 new apprenticeships.
Bombardier will deliver rolling stock - including 65 trains - for Crossrail, which will link the east and west sides of London.
It comes after Bombardier controversially missed out on a £1.4bn contract for the Thameslink project in favour of German firm Siemens in 2011, forcing the firm to announce 1,400 job cuts.
This is the first picture of what the new Crossrail trains set to be manufactured at Bombardier's Derby plant will look like.
The firm was awarded the contract to build 65 trains for the project, beating competition from Japanese company Hitachi and Spain's CAF.