Changes to the building regulations relating to hot water supply and systems, specifically a requirement that hot water storage systems must include a feature which  prevents the temperature of the stored water exceeding 100 degrees C and that any discharge safety devices must be to a location where it is visible but not cause danger to people in the building.

They are still shown in the May 2017 timetable and although I do not have a 2018 timetable in front of me, the change was almost certainly in December 2019 when the timetable was recast to give a regular stopping pattern for most services to Plymouth/Penzance.  I believe Virgin did the same with their named trains on both XC^▸ (Cross Country Trains (franchise)) and West Coast back in the 2000s.

The only named train shown in the December 2019 D timetbale is the Night Riviera.

One change I note is that the the first direct service of the day from stations on the Berks & Hants to Plymouth 1C85 (1436 from Paddington) will run to Paignton instead (arriving at 1744).  It will then form 1A98 departing from Paignton at 1902 (instead of the 1857 from Plymouth) and calling at Torquay, Torre, Newton Abbot, Teignmouth, Dawlish and Dawlish Warren where it is overtaken by 2U32 Penzance to Cardiff Central (not sure I've ever seen an intercity service to London getting overtaken by a regional service at Dawlish Warren before).  After reaching Exeter it then runs as previously to Paddington.

It's only fully hourly as far as Bristol, there are some two hours gaps west of there.

https://www.gov.uk/government/publications/great-western-prior-information-notice

The DfT^» (Department for Transport - about) have published a prior information notice for a direct award which is anticipated to be for a duration of between three and six years.

6 is Penzance.

The 1982 WTT^▸ (Working Time-Table) shows a DMU^▸ (Diesel Multiple Unit) service from Reading to Bedwyn running roughly every 2 hours off peak and the 1989 Paddington Station Workings do not show any Paddington to Bedwyn services off peak so it would seem to be the case that the regular service from Paddington was not introduced until the arrival of the turbos.  I wonder if the turbo service from Paddington was initially all stations west of Reading or if the Reading to Newbury shuttle was introduced at the same time, giving Newbury 2 trains per hour from Reading off peak (quite an improvement from what was on offer in 1982)?

In the case of Exeter to Plymouth/Penzance, it may well be that the sea wall section would make any scheme prohibitively expensive but the one that really seems to stand out is Worcester to Hereford.  Is there anything on this route which would make electrification difficult?

It does say though that as numbers recover, long distance operators will have more autonomy and commercial freedom (page 31).  It expands on this on page 58 by saying:

Only seven which are on the list but I have visited two which are now closed:  North Woolwich and Tilbury Riverside.

Considering much of Europe uses speed-based rather than route-based signalling, would there even have been an explicit route indication shown to the driver in this case?

3 is Glasgow Central.

The October 1975 Paddington Station Workings book shows the 2345 as having one SLC^▸ (Service Level Commitment) is the formation which was detached at Exeter along with a GUV (Cars).  I expect this sleeping coach was for the use of Motorail passengers travelling to Exeter.

Sorry, wasn't thinking about the journey planner.  Hopefully they will update this soon now they have published the timetables.