Incomplete journeys can be made when passengers do not swipe either in or out using their Oyster card or contactless debit card at a station.

A maximum fare - up to £8.90 per rail journey - is then charged as it is not possible to assess the correct fare without both touch-in and touch-out data. There were 15.1m of these journeys in 2015, according to a freedom of information request.

TfL says that such charging “protects all users of public transport from the cost of fare evasion", but the money they raise from it has been criticised by consumer groups for “profiting from consumer confusion”.