Every day, millions of passengers travel on trains where the only member of staff on board is in the driving seat Sign up to Simon Calder’s free travel email for expert advice and money-saving discounts Get Simon Calder’s Travel email Get Simon Calder’s Travel email Email * SIGN UP I would like to be emailed about offers, events and updates from The Independent. Read our Privacy notice The RMT union is threatening industrial action against Chiltern Railways in a row about driver-only operation (