Actual work has finally started on the huge £5.5 billion Thameslink upgrading programme, nearly 20 years after the scheme was first proposed.

After a series of setbacks and delays, construction work has kicked off in Bedfordshire on the Thameslink route operated by First Capital Connect.

The scheme will be one of the biggest rail projects ever in the UK, taking an estimated 40 million hours to complete.

The go-ahead came when rail minister Tom Harris visited Luton Airport Parkway station and symbolically dug into the ground where platforms are to be extended to take 12-car trains.

Tom Harris said: “It is hard work like this today which will deliver benefits to passengers across the South East in the future, including longer trains from 2011.”

But the start of work came as a row over what is claimed to be a distinct North/South divide in rail investment in Britain raged in the Commons Transport Select Committee.

Transport secretary Ruth Kelly faced tough questioning from a Northern Labour MP over a report which shows that rail investment in the south of the country is far greater than in the north.

The Thameslink launch ceremony at Luton in late October came just three months after the rail project was announced by Network Rail as the centrepiece of the company’s spending plans until 2014.

A team of 180 people led by Andrew Mitchell, Network Rail’s Thameslink programme director, has been working on the project, which will expand the current route from Bedford to Brighton to destinations such as King’s Lynn, Peterborough, Littlehampton and Dartford.

The project will tackle overcrowding on some of the UK’s busiest routes, such as the Brighton main line and the East Coast main line, by enabling longer and more direct trains to run to more destinations.

The scheme will be completed by the end of 2015 and has been planned to deliver benefits for passengers before the Olympic Games.

Stations will be rebuilt along the route and bottlenecks removed at Blackfriars and London Bridge.

Andrew Mitchell said: “This is now not an aspiration – it is happening right now, here today. Network Rail will be working closely with First Capital Connect to deliver these improvements at Luton Airport Parkway and a better railway for everyone in the South East.”

In a recent exclusive interview with Railnews, Network Rail’s chief executive Iain Coucher likened it to engineers carrying out “open-heart surgery on one of the busiest bits of railway in Europe”.

The programme will also deliver a direct link to St Pancras International and Eurostar services to Europe, with a new London commuter station due to be opened in December.

Luton Airport Parkway is the first station of 23 to have its platforms extended on the Thameslink route before 2011.

Overall, the scheme will see some three miles of platforms lengthened and will enable a 50 per cent increase in capacity through longer trains and more services.

Elaine Holt, managing director, First Capital Connect, said: “When the entire Thameslink programme is completed, there will be 24 trains per hour through the heart of central London, the majority of which will be brand new trains.”