Advances from Plymouth, they are indeed available, just like there are from anywhere a similar distance from London in the UK on a mainline: ECML. MML. WCML...
But if the trains are full anyway because of the level of demand for travel to/from the West Country which you insist is there, then there should be no need whatever to sell cheap tickets from Devon and Cornwall to fill those seats.
And if they didn't, then there might be more seats available for people along the B&H, which might be a more cost-effective way of serving those stations than setting up an expensive semi-fast operation, which neither BR, nor FGW since, has shown much inclination to do, beyond the odd train here and there.
You can get advances from places a similar distance from London isn't much of an answer is it?
Oxford isn't a long way from London but FGW sell advances. Virgin has to fill three 600-seat trains per hour between London and Birmingham and London and Manchester, so not exactly shocking they need to sell advances to help fill them. EC have an awful lot of trains running up and down too, so again lots of seats to fill, so they take steps to do that in the shape of advances, so do EMT.
By contrast, there aren't lots of West Country trains, they are very busy all the time apparently, so why on earth do FGW need to sell heavily-discounted fares?
The Walrus said:
You mention twice that Cotswolds services are busy between Oxford and London. This is very true but still means they may be running the majority of the journey to Worcester with lighter loadings. It's like the London-Bedwyns; busy ti Newbury, lightly loaded west of Newbury. Doesn't mean it's worth running a Hst full to Newbury then empty to Bedwy and back!
No I wouldn't want to spend 3 hours on a turbo, but then I wouldn't want to spend Bedwyn-London on a turbo either. But realistically, how many travel to Hereford via the Cotswolds Line?
It's not like London-Bedwyns - it takes about 75 minutes to get to Bedwyn. To Worcester is two hours plus, Hereford more. Newbury to Bedwyn is a dozen miles. Oxford is near-enough half way on a 120-mile journey between London and Worcester. And while Worcester and Hereford aren't huge places, they still beat population in B&H-land hands down, before you add in the Oxford and London commuter and leisure traffic at the eastern end of the line
Just over an hour on a 166, so long as it is not crush-loaded, is perfectly acceptable, though that's about the limit of their capabilities. That's why the return of the 180s was so popular - even if they still aren't reliable enough - they are pretty much the ideal train for off-peak and contra-peak work on the Cotswold Line, with a handy seating capacity, but not the overkill an HST represents at such times, and inter-city standard accommodation.
Many Cotswold Line trains have lighter loads west of Oxford, but some of the peak HSTs reach Oxford full off the Cotswold Line and leave Oxford full in the opposite direction in the late afternoon and early evening. Other services can also load heavily - I don't recommend the first off-peak train towards London if worked by a 166 in half-term. Getting on for 350 people on one arriving at Oxford is not nice.
You might be surprised how many people do go all the way to/from Hereford - at least in the peaks (and back to London on Sundays). No need to change, which you do at Newport, with the risks that banking on what are sometimes five-minute connections involves. Travel regularly on the 17.22, 17.50 and 18.22 Cotswold Line departures from Paddington or Oxford and it is obvious the first and last, which go all the way to Hereford, are always busier than the 17.50, which ends at Worcester. And the 19.22 has got busier since it also started running to Hereford, rather than turning back at Malvern.