Commuters on London Overground orbital rail
10 December 2012 Last updated at 21:43 GMT
Commuters have been experiencing what has been referred to as the "M25 of rail".
The final stretch of the London Overground line has linked Surrey Quays with Clapham Junction, which means the capital now has its first orbital line since 1884.
London Mayor Boris Johnson, has used the launch to argue for more control of the capital's railways.
London's Transport Commissioner Peter Hendy and Transport Secretary Patrick McLoughlin also spoke about the new service.