By Guy Taylor A trail of off-peak tube and train fares will start today and run for three months, as part of a trial aimed at encouraging commuters back to the city centre. The experiment will run between March 8 and May 31, covering pay-as-you-go contactless and oyster fares on London’s Underground and rail network, as well as parts of the South East. It was announced by Mayor Sadiq Khan in late January after he struck a deal with private operators to slash peak fares. Some £24m has been allocated from the Mayoral budget to cover the cost of off-peak tube fares for TfL and national rail opera…