ES News email The latest headlines in your inbox twice a day Monday - Friday plus breaking news updates Enter your email address Continue Please enter an email address Email address is invalid Fill out this field Email address is invalid You already have an account. Please log in Register with your social account or click here to log in I would like to receive lunchtime headlines Monday - Friday plus breaking news alerts, by email Update newsletter preferences

Nigel Farage has revealed that he refuses to buy an Oyster card in case it is used to spy on him.

The Ukip leader said he always chooses a cardboard ticket to prevent the authorities “knowing where I am going”.

His comments threw a spotlight on the increasing use of Oyster data to investigate crimes and study the movement of suspects or victims.

Privacy campaigners said the MEP’s concerns were justified, because of a steep increase in requests by the authorities to see where people travel to and from.

Speaking to reporters, Mr Farage said: “I won’t even buy an Oyster card because I don’t want people knowing where I am going. I buy a daily ticket.”

When a questioner pointed out that Oyster cards do not have to be registered in the owner’s name, Mr Farage said he still did not trust them. “Well you never know,” he said. “They are tracking your movements, dear boy, they can.”

Labour MP Stephen Pound said Mr Farage was showing “an interesting level of paranoia” and suggested his Oyster might reveal him to be “on the District Line to Barking - his natural constituency”.

However, privacy campaigner Heather Brooke said Mr Farage was right to assume that his travel could be tracked, even if he had not registered a card. “Increasingly, Oyster cards are tied to your credit card or other identifying material,” she said. “It is difficult to have a blank Oyster card that is not linked to you.”

A staggering 43 million Oyster cards have been issued since the swipe system was introduced 10 years ago and they are now used for 80 per cent of journeys by bus, train and Underground in London. Each trip is recorded on the system’s computer and the details held for eight weeks.

Police use of Oyster data has rocketed since the cards were launched in 2003. In 2004, there were just seven requests made by police to access records. In 2010 Scotland Yard made 6,258 requests.

A Yard spokesman said: “During the course of a criminal or a missing person investigation the investigating officer identifies a number of lines of inquiry.

“Each case is looked at individually but such information could be used to build up a picture of a person’s movements.”

Oyster information was used to investigate the murder of City lawyer Thomas ap Rhys Pryce, who was stabbed in Willesden Green, north west London, in 2006.

Records showed someone attempted to use his Oyster card in Kensal Green tube station the day after he was killed.

A 2009 TV documentary, The Force, revealed how police caught the murderer of a London hotel worker with the help of Oyster journey data.

A TfL spokesman said data was only kept so that customers can check their own journey history. “We do not hold any data for more than eight weeks,” she said.