Did this train ever stop at Dean or Dunbridge in the Wessex Trains days? If it did, that may well explain how it came in to being.
That's interesting feedback; I'm seeing no "smoking gun" as we have for the apparently-absurd 11:11 Westbury to Southampton (10 minutes behind the 11:01 and with just one extra stop) - the smoking gun being the large number of connecting passengers arriving into Westbury from the South West at about 11:04.
In the 2002 / 2003 timetable, the southbound train ran at 17:52 rather than 18:52 from Swindon and it was the main evening commuter TransWilts service. And it called at Dean at 19:23 and Dunbridge at 19:29, reaching Southampton via Eastleigh and Southampton Airport at 19:58. It carried on at 20:00 (to Swindon at 21:53) NOT calling Dean or Dunbridge, but it did stop at Dilton Marsh.
From December 2006, the train ran an hour later with the withdrawal from service of the unit that had been running it, being formed instead (as it is these days) of the 17:40 from Cheltenham Spa, and running direct from Romsey to Southampton rather than via Southampton Airport. It paused for 10 minutes (in olden and current times) at Westbury to provide a connection from passengers arriving from Bristol and Bath on a Westbury-terminating local service - I suspect primarily for Warminster and Salisbury commuters; I don't know what loadings were like south of Salisbury in those days either.
Passenger numbers from Swindon to Melksham / Trowbridge / Westbury plunged at December 2006 as the 18:44 departure for a homeward return commute was too late - especially as the remaining matching up service arrived at 07:48 into Swindon - but that's not the story I'm looking at here and I've told it before.
Back to Dunbridge / Dean. The 20:00 off Southampton (now 21:20) didn't call at Dunbridge / Dean (see above) - but the 20:09 (a Portsmouth - Cardiff train) did. On the other hand, the Portsmouth - Cardiff missed out Dilton Marsh. The Swindon end of the service was very quiet, and the final run - the 22:01 Swindon to Westbury was quite quiet too but provided a useful end-of-day fallback for commuters late back from work. At present, the 21:44
HST▸ from Swindon, connecting into the 234 bus at Chippenham which accepts rail tickets, provides for this flow and combines bus / train passengers to ensure there's at least one public transport service in the late evening on that corridor.
I don't know where I'm going with this thread - except that I'm in a learning process to help being well informed for future changes. I know the "why" for most of the
FGW▸ extras south of Salisbury, but this one has puzzled me. But then by 20:14 in the evening, there's no great stock shortage and no other burning flow it could mop up if it did something else. In current times, a late TransWilts run would be better resources via an extra run of the 'local' 153 - and please note this should not be read as a proposal nor as a word against any such proposal. Another definite "don't know" within research and learning.
Network SouthEast - many thanks for helping in this understanding; inevitably there will be changes / knock ons "all the way to Brighton" when timetables of long distance expresses change with
GWML▸ electrification, and it's good for those of us up in Wilts to be aware of the wider picture as we listen to proposals and perhaps provide tuning feedback.