The Waterloo and City line, which connects the City with Waterloo Station will for the first time run late night services.
Currently trains stop at 9.45pm in the week, 6.30pm on Saturdays and there are none on Sundays. But from next month, in the week the service will run every three and a half minutes until 9.30pm, every six minutes until 11.30pm and every 10 minutes until midnight.
On Saturdays the service will be extended to 11.30pm.
The London Fire Brigade was called to Waterloo Station this evening, to carry out safety checks on the concourse floor.
They left without needing to take any action.
A spokesman for Network Rail said that a section of the floor was slightly raised - by a couple of inches - and that an area been cordoned off between platforms 15 and 18, while engineers examined it.
Services from the station are not being disrupted.
Trains from Waterloo Station are being delayed by up to 50 minutes.
The delays- which are due to an incident in Wimbledon which is being dealt with by the emergency services- are likely to continue until the end of the day.
Passengers are being advised to use alternative routes where possible.