North London Line fares are set to double in January.

While Mayor of London Ken Livingstone has frozen most prices for those using Oyster cards from next year, passengers paying cash for tickets will see the cost of trips within a single zone rocket from £1.30 to £3.

And because Oyster readers have not been installed along the North London Line, passengers cannot use their pre-pay Oyster cards and will be forced to buy the more expensive cash ticket.

A single zone journey, such as a trip from Crouch Hill to Hampstead Heath, with an Oyster card would cost £1.30.

Oyster travelcards, which are allowed on the North London Line despite the lack of sensors, will still be able to be used.

Darren Johnson, Green Party London Assembly member, has branded the price hikes unfair', and believes that Mr Livingstone should suspend the inflation-busting rises until the Oyster sensors are installed.

Mr Johnson said: "It is quite unfair people will be hit hard. As long as there are so many anomalies, I just think it's so unfair to have a massive increase in fares. It needs a re-think."

A spokesman for Transport for London (TfL) said that it had done all it could to get the readers installed, but had not received the go-ahead from the train companies.

"It will be a source of frustration," he said. "We have done everything: we have offered to install the readers and maintain them. We haven't been taken up by anyone."

Mr Livingstone is discussing with the Department for Transport whether he can control National Rail services within London, and the spokesman said that if this gets the green light, then the equipment will be put in place.

A representative for Silverlink, which runs the North London Line, said that the discussion had been slow moving and they had heard little from TfL recently, but talks were held on Tuesday.

"We want to make travel as easy as possible," he said. "The readers will not be in by January, but we want to get going as quickly as possible."