Heart of Wales is also following the Sunday timetable of 2 per day as well and sets will need to swap at some point from Canton to Swansea for these. I think one day I saw a 153 on what would have been a Swansea-Manchester service also, no idea if It was swapped at Cardiff or if something may have been attached to it in Cardiff.I think the 153s are being used due to reduced demand but I wonder if they are any cheaper than a 150 to run
Also I know the Pembroke dock branch doesn't see a train till 1 currently so there's 1 153 in the morning sitting spare which probably runs somewhere around Cardiff or Swansea