Stephen Joseph, chief executive of the Campaign for Better Transport, has welcomed the announcement of a trial of season tickets for part-time workers in London.
He is calling for the scheme to be introduced quickly and rolled out across the commuter network.
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Officers believe the three assaults are linked and are appealing for information about the suspect.
Nine addresses in Lewisham were searched and 13 arrests made early on Tuesday morning in a planned, intelligence-led operation.
The Purple Rain singer died in April 2016