I've downloaded the XC May 2019 - December 2019 timetable. However, a reliable person has informed me (before I looked at the timetable properly) that the 09:35 from Penzance to Manchester Piccadilly starts at Plymouth at 11:50.
In its place, the 11:24 (to be exact) from Plymouth to Dundee doesn't just start from Penzance at 09:25, and reduce journey times for those travelling to between (including the 2 stations) Totnes - Birmingham New Street, but is formed of an HST (subject to availability) on Fridays on the whole trip of just over 12-hours!
A few extra Manchester to Bristol services are now extended to and from Exeter St Davids too.
Regarding the new Penzance to Dundee service - an HST should hopefully reduce overcrowding from the GWR London services between Penzance and Taunton as well as in general obviously and with any luck should have more people wanting to travel to the North
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If the 09:25 from Penzance to Dundee is an HST on Fridays all-year round then I might just catch that from Birmingham New Street to Edinburgh next year.
The 06:32 from Dundee to Plymouth is an HST on Mondays and Fridays - 17:25 from Plymouth to Leeds on Fridays is an HST.
The HST is subject to availability.
XC haven't said but I've been told this.
Weirdly, a 7-coach HST has more seats than an 8-coach Voyager!