Flexible train tickets proved popular with commuters during a trial period, Hove Labour MP Peter Kyle said.
And government ministers should give a clear commitment to make them available for all Southern passengers, he added.
Mr Kyle was responding to the publication of a report about the trial scheme.
He said: “This report clearly shows the flexible season ticket pilot was a massive success with Southern commuters.
“It further underlines why we need to see action now and I will continue to press government ministers and rail operators to clearly commit to introduce this in full across the network without delay.”
The report was produced by Southern as an end-of-project evaluation of the flexible ticketing scheme pilot that was carried out last year.
Southern found that “customers were … very receptive to having flexible passes, which could be carried forward for future travel at no extra cost”.
In addition, Mr Kyle said, more than 90 per cent of those taking part in the trial believed that they had saved money with the “flexiSeason” ticket.
