A new era for King’s Cross station is about to begin as a sweeping half dome roof and new one-way system to reduce congestion will be officially opened by Boris Johnson this evening (Wednesday, March 14).

The Mayor of London and the transport secretary Justine Greening will speak at the official opening event at 6pm.

But passengers will not gain access to previously unseen areas of the 19th century station until it is unveiled to the public after three years building work next Monday (March 19).

The station’s western concourse has a new entrance hall accessed from Pancras Road, close to St Pancras Station.

The highlight of the new entrance is its lattice-patterned half dome shaped roof, which allows light to stream into the station.

Graham Goodwin, of Network Rail, said: “There is a real wow factor. We’re really proud.”

He added: “You literally have a window to history. We’re lucky that English Heritage have been very pragmatic and we’ve been able to work with what the Victorians did and add what we need to make it last another 100 years.”

Commuters will use the new entrance hall instead of the existing one in Euston Road, which will become the station exit.

The changes are designed to ease congestion and to improve the interchange between King’s Cross national rail and underground lines, and St Pancras station.

It is the first step of a wider �440million programme to demolish the much criticised “dingy shed” entrance in Euston Road and replace it with an open air plaza twice the size of Leicester Square.

The roof of the old entrance in Euston Road is due to be taken down this autumn and the new plaza created in 2013.

Preserving and enhancing the historic character of the 1852 Grade I listed building has been a priority.

The new ticket hall and new station pub occupy areas which have not been open to the public since Victorian times.

The works have also restored the “bomb gap” area which was demolished during the Second World War.

Pauline Nee, of John McAslan & Partners, the architects in charge of the build, said: “We want people to remember the historic building.

“We’re bringing them closer to the historic building at the same time as engaging them with the best of the modern building.”

Mr Goodwin added: “There will be a learning curve and commuters are going to have to learn to use the station in a very different way.”