Commuters are confused by a new car parking regime at Oxford railway station designed to drive out shoppers.

Rail passengers can still use the pay-and-display system - but it will cost them £20 per day if they are travelling before 10am.

They can cut the cost to £4.50 per day by using a new hi-tech telephone system.

But for the past week, drivers using the long-stay car park in Becket Street say they have been faced with a brainteaser before boarding the train.

Instead of using pay-and-display, they are encouraged to use RingGo, which requires the use of a mobile phone and debit or credit card.

Zahra Akkerhuys, a spokesman for OxRail Action, which campaigns on behalf of commuters, said: "The new system is far too complicated and involves reading out your credit card number, either on the platform or on the train.

"I saw lots of people wandering around the car park looking very confused and a guy was handing them a leaflet explaining the new system. Speed is of the essence when you're a commuter and this system takes far too long.

"Pay-and-display is simple, but you're not going to choose that if it costs you £20. This was the first time I have driven to Oxford station and I won't be doing it again."

Grant Stevenson, 38, from Carterton, who works for British Telecom, added: "It's not nice to have to give out your credit card number on the platform. Pay-and-display was much more convenient."

Until last week, commuters were able to buy a £4 daily ticket from the pay-and-display machines. Now, using the new phone system, they can park all day for £4.50 on weekdays.

A pay-and-display ticket bought between 10am and 1pm costs £15, between 1pm and 5pm £10, and between 5pm and midnight £5.

The new system, operated by Airport Parking Corporation of America (Apcoa) for station operator First Great Western, was introduced to stop shoppers and office workers using parking spaces intended for rail passengers. All-day parking at the Westgate car park costs £18.20.

Hameed Khan, of Apcoa, who handed out leaflets explaining the new system, said: "This is a way of removing non-commuters from the car park.

"I have had to explain the situation to some customers, because they have been putting in £4.50 and then they are frustrated when they do not get a ticket."

Graham Smith, the city council's car park manager, said: "We were aware that the long-stay car park was being abused."