A rail operator is cracking down on fare dodgers by introducing a penalty scheme.
Thameslink, which runs services from Brighton through London to Bedford, is bringing in the penalty fares for the first time since 1997.
The scheme will operate between Brighton and East Croydon.
Any passenger found without a valid ticket will either pay the ticket price plus £10 or be fined twice the cost of the journey made plus the cost of the remaining journey, whichever is greater.
Revenue protection officers will be asked to use discretion in assessing why people are travelling without a ticket.
Thameslink said it understood there might be extenuating circumstances preventing a passenger buying a ticket in advance.
Keith Jipps, Thameslink's retail manager, said: "We have made great inroads into the fare evasion problem in recent years.
"More staff and ticket barriers have contributed to this improvement.
"It is interesting to note that there has also been a corresponding decline in hooliganism on stations and trains as a result of these actions."
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