The newly-opened concourse at one of London's busiest railway stations will not meet demand in the long term, the head of Network Rail has said.

Two-thirds of the £1 billion redevelopment at London Bridge station, which was unveiled on Monday, will enable passengers to access all platforms from one level for the first time. Once complete, the concourse will be bigger than the pitch at Wembley Stadium.

But Network Rail (NR) chief Mark Carne, speaking at the opening of the new development, said he was not confident it would meet the needs of passengers in the future as the number of people using the station swells.

"There's no doubt at all that this is not going to meet the demand for 50 years. As the passenger demand continues to grow, we will need to continue to invest and there will need to be significant investment in the railways over the next 20 years just to keep pace," he told the Press Association.

The Herald:

Members of the public try out the new concourse and platforms at London Bridge Station. Photo: PA

Mr Carne said there had been a "staggering" growth in passenger numbers on services that pass through London Bridge of 5% to 6% every year.

"Since this project was originally approved, the passenger numbers have grown by 35%. So it's a constant challenge to keep pace with demand but that's a problem of success and I think Britain's railways are a huge success story."

Over the bank holiday weekend, the project's construction site was moved away from the Southern and future Thameslink platforms to focus on the north of the station, used by Southeastern.

Trains into Charing Cross have now begun calling at London Bridge for the first time since January 2015, but Cannon Street trains stopped serving the station on Friday and will not resume until January 2018.

The south London station has suffered incidents of severe overcrowding since work began four years ago. Reconfiguring the complex track layout around the station has exacerbated the impact of any delays.

NR, which owns and operates Britain's railway tracks, signals and busiest stations, including London Bridge, said the improvements will allow up to 24 Thameslink trains an hour to run through the capital - equivalent to one every two to three minutes - compared with just eight previously.

The Herald:

Members of the public try out the new concourse and platforms at London Bridge Station. Photo: PA

There will also be more connections to Gatwick and Luton Airports, and beyond to Peterborough and Cambridge.

Mr Carne said he was "very excited" about the changes and apologised to passengers who had been affected by the delays.

"I would like to thank passengers actually for their patience over the last couple of years that we've been doing this but I hope that they will now really see that it's been worth it because this is a real transformation."

The station's transformation is part of a £7 billion programme to improve the Thameslink network for people travelling across London. It was originally called Thameslink 2000, but, after series of delays, the project is now expected to be completed in 2018.