Reason revealed for major West Sussex delays: Line reopens between Worthing, Chichester and Brighton
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Southern Rail said at 6am that a trespass incident on the railway meant that all lines had to be closed.
As a result, trains were cancelled, delayed or revised.
"All trains are at a stand in the area in the interest of safety.
"The power to the lines has been switched off whilst emergency teams respond. No trains will be able to move between Worthing and Brighton until further notice.”
Power was restored and all lines had reopened by 6.30am.
“Please continue to check journey planners, as it may still take up to 15 minutes longer than usual to reach your destination,” a Southern spokesperson said.
In an update at 7.30am, Southern added: “Disruption caused by trespassers on the railway earlier today between Worthing and Barnham has now ended. Services are no longer affected by this problem.”