Southern Rail passengers today face disruption amid a 24-hour strike in an ongoing dispute over driver-only trains.
Members of the RMT Union are staging the walk-out while it awaits talks with rail bosses over staff safety.
The rail provider is operating limited service on routes between Clapham Junction and Watford Junction, London and Guildford and Brighton and Hove.
Some services around Bognor Regis, Littlehampton, Brighton, West Worthing and Portsmouth will be cancelled, Southern Rail said.
Passengers affected in the capital are advised to use rail services between Euston and Milton Keynes, the London Overground from Clapham Junction, the Tube and Thameslink services.
January Rail Strike - In pictures
Southern said they expect to run a normal service on all other routes.
A spokesman said: "We expect to run a normal service on most routes.
"Only a week before this announcement, the RMT rejected proposals we made about the basis for finding a settlement and we renew our call for the union to end this pointless dispute.
"The RMT should face the reality that the changes they are objecting to were successfully introduced a year ago."
RMT General Secretary Mick Cash added: "Our members stand solid and united again today in the fight for passenger safety and access on Southern Rail in Britain's longest-running industrial dispute.
"The sheer grit and determination of our members on Southern to put public safety before private profit over the past two years of this dispute is a credit to the trade union movement and the communities they are standing up for."
"We are now receiving regular reports of trains running without a guard or OBS on board on Southern Rail and of disabled passengers being denied support and access and the routine safety of passengers being compromised.
"The scandal of Southern Rail cannot be allowed to continue and GTR should get out of their bunker and get back round the table with the union."
