Angry rail passengers have accused train operator South Central of not playing fair over fares.
They say the firm should not have charged the full weekday ticket price while failing to run a weekday timetable after the Christmas break.
Passengers who travelled to London yesterday and on Thursday were charged the full £26.80p return peak fare for a reduced service - the basic Saturday service with a few additional trains.
On Saturdays and Sundays the rail company does not charge peak time fares.
There were arguments at ticket offices as passengers needing to travel during the rush hour on December 27 and 28 queried ticket prices.
Commuter Richard Marris was livid to be charged the full peak travel price for his return ticket from Preston Park station.
The 35-year-old IT worker from Withdean said: "They should not be running a Saturday service and then charging full fares as if it was a weekday with additional morning rush hour trains.
"When I asked at the ticket office why they were charging weekday prices for a Saturday service I was told, 'Because it is Thursday, mate'.
"It cost me nearly £19 more to travel up to London on Thursday and Friday than on a Saturday because I had to spend an extra £3 for the Underground.
"I can get an all-in ticket which includes the Underground for £11.10 with a Network Railcard on a Saturday. I normally have a season ticket, but it was not worth it in the days between Christmas and the New Year.
"I don't think South Central or any other rail company should be able to get away with this."
Regular Brighton to London commuter Dr Paul Dawson, of Centurion Road, Brighton, was also angry.
He declared: "This is unfair. If they run a Saturday service they should charge Saturday prices."
A South Central spokesman defended the decision.
He said: "Fewer people travel during the early morning in the days after Christmas, so we have an enhanced Saturday service in common with other rail operators.
"All operators, including London Underground are operating the same charging policy. Thursday and Friday were weekdays, so we charged the full price.
"We were running some additional trains to the Saturday timetable."
Mike Hewitson, secretary of the Rail Passengers' Committee for Southern England said: "The charging of the full weekday fares for the days after Christmas goes back to the days of British Rail.
"It is within the franchise conditions of South Central that they are allowed to tailor the service to meet demand at different times of the year.
"At present passengers can do nothing about this as rail companies are acting in accordance with their franchise conditions.
"We would like them to make people more aware of their fare charging structures so confusion does not arise."
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