Gordon Brown cast the cares of the Westminster expenses scandal aside for a while today by celebrating the start of major construction work on the £16 billion cross-London Crossrail scheme.
The Prime Minister appeared relaxed as he joined Rail Minister Lord Adonis and London Mayor Boris Johnson at Canary Wharf in London Docklands as a foundation for a new Crossrail station was laid.
Mr Brown said: "Many people said it would never be built, but today we are celebrating a defining moment for London as Crossrail's construction gets under way."
Running from as far west as Maidenhead in Berkshire, the Crossrail main line railway will go through central London as far east as Shenfield in Essex, with links to Heathrow Airport in west London and to Abbey Wood in south London.
At peak times, 24 10-car trains will run an hour in a scheme that was first mooted in 1974 but was scrapped on cost grounds by the Conservative Government in 1994.
Mr Brown said today: "Crossrail will not only mean fast journey times across the capital and beyond, it will also bring a massive economic boost to the city, creating thousands of jobs and adding at least £20 billion to our economy.
"Investment in to important projects like Crossrail, the largest construction project in Europe, is vital to create and protect jobs as well as supporting business, so we can grow our way out of recession and ensure a strong future for London and the country as a whole.
Before today's opening ceremony Mr Brown, Lord Adonis and Mr Johnson were shown large scale models of the Crossrail project, including the new station being built at Canary Wharf - one of a number of new stations on the 73-mile long railway.
There have been concerns that the Conservatives could abandon the project because of the economic conditions should the party win the next general election.
However, Mr Johnson is determined that the scheme goes ahead.
He said today: "The years of hesitation, irresolution and vacillations are over, the shovels have tasted earth and the construction of a railway that is crucial to the economic prosperity of this great city has begun.
"This amazing project will create and support thousands of jobs, relieve congestion and provide a high-speed link between east and west of London.
"When the first of Crossrail's chariots glide smoothly along its lines in 2017 it will change the face of transport in London and the south east forever."
Mr Johnson said that the 1994 decision to abandon Crossrail had been a "cardinal mistake" and it must not happen again.
Mr Brown said it was a great day for Canary Wharf, for public transport, for engineering, for London and for the concept of partnerships.
He said that today's opening showed that no barriers were going to stand in the way of the project and that it was a "signal of faith in the future" adding: "If you don't invest in the future you have no future."
Politicians and guests then moved to the construction site of the new Canary Wharf station where the first of nearly 400 18.5 metre tall steel piles was sunk in to the ground.
With the railway running through tunnels in central London, there will be nine new stations built underground in central London, Docklands and Woolwich in south London as well as 11 major reconstructions of national rail stations along the route.
Preparatory work has already started at Tottenham Court Road station in central London and preparatory work gets under way later this year at Farringdon and Paddington stations.
The Department for Transport will be responsible for £5.6bn of funding for the project with Transport for London responsible for £7.7bn.
The rest of the money is coming from the private sector with airport operator BAA supplying £230m and the Corporation of London funding £200m.
Mr Johnson pressed a button and the steel pile sank into the dock on which the new Canary Wharf Crossrail station will be built.
Afterwards, he said it would be "inconceivable" for any incoming Conservative government to tamper with the Crossrail project.
He repeated his belief that the Tories had been mistaken to scrap Crossrail in 1994 and this mistake had "led to overcrowding and many sweaty journeys on the Tube".
Mr Johnson went on: "I'm absolutely sure that no government in their right minds would tamper with this scheme."
He said he was not going into any detail of any discussions he might have had with the Conservatives concerning the future of Crossrail but he had "every reason to think" that a future Conservative government would understand the importance of the project.
He added that it would be the "height of folly" for any government to abandon Crossrail.