Make no mistake ... it should be easy - VERY easy - to slot in a good Swindon to Westbury service, even at this late stage of timetable planning 

The early morning train off the Stroud Valley already supplies the stock for the 06:20 to Westbury, and indeed it can continue to supply the stock ... couple on a "153" unit from its home base. At the end of the day, the "153" returns back to its home base attached to the last local service on the Stroud Valley. No extra empty stock workings, no extra crews required to get the unit to a servicing point.

This scheme would loose us the 05:37 off Westbury / 05:52 off Melksham - a pity, but not usually a very busy train. It would gain us an extra evening train up from Westbury, making days in London / evening returns much more attractive.

If the new FGW timetable turns out to be truely "clockface" as has been their aim, then the Swindon - Westbury under this scheme will automatically be clockface too.   If  the FGW service isn't as regular as they had hoped, there may be irregularities on the "West Wilts Flyer".

A further comment ... for pathing issues on the main lines (Thingley - Swindon and Bradford South - Westbury), a few minutes pause as Melksham would solve any issues;  it wouldn't be blocking, and a slightly leisurely schedule would ensure crisp timekeeping on the busier sections.

Actually, NO, Nick, I haven't mentioned it; I've been leaving the experts to work out the detailed logistics of their service. I've felt it would be rather like going to a bakery and telling them not only what I want to buy and what their customers want, but also how to do the baking.

But ... the time comes that it might be worth pointing out how seamlessly the extra service would fit in ...