Thanks
@TimboM that all makes sense. Suffice to say the 153xx coaches must be worked that little bit harder than the other coaches. I now understand how critical the 150xx coach is !.
One question - How do the FortWilliam-Edinburgh seated coaches (150xx & 151xx) get swapped ?.
Would Polmadie send out to Edinburgh the replacement two coaches for exchange at Edinburgh in the wee hours ?.
I suppose an easier route to achieve this is for the two seated coaches to end up staying on the Highlander and what was on the main leg of the Highlander to end up on the FortWilliam-Edinburgh shuttle. I understand the shunting at Edinburgh for the North bound highlander is rather tight so it would have to happen at Edinburgh when all three portions are arriving at Edinburgh to form up for onward travel South. Then when Wembley sends them back on the Lowlander Polmadie gets em !. Or is that too complicated !.