 However, the then Conservative government, which was preparing the company for privatisation, baulked at the cost (estimated at over £1bn).In the end, two different proprietary systems were trialled, TBL on the Great Western Main Line and SELCAB on the Chiltern Main Line, but neither system was rolled out across the network.Today, all Great Western Railway HSTs are fitted with ATP and are not permitted to carry passengers unless the system is functioning.