It is the beginning of the end of paper rail tickets for some Southern passengers travelling into London.
Commuters using the Brighton line into the capital will be able to use smart-cards, similar to Oyster-cards, at East Croydon, Clapham Junction, London Victoria and London Bridge.
The scheme will be widened out to all London stations as of next year.
Baroness Kramer launched the new scheme yesterday.
More top news
Patchy rain tonight ahead of another cloudy and breezy day tomorrow. Rain and stronger winds arriving from the west tomorrow evening.
Staying cloudy with patchy rain tonight. Rain and stronger winds arriving from the west tomorrow evening.
Cloudy and breezy with rain arriving from the west later.