Shown tonight, 30/08/2019, on channel 5. Featured the South African blue train and others. It was reported that the blue train was very expensive, but arguably worth it for the luxury.
In fact the blue train was a lot cheaper per mile than GWR▸
An interesting but potentially invalid comparison. You have taken a GWR route on which you are eating pretty much the whole way ... and compared in to the total journey in South Africa where (one hopes) you would pause decently between your three meals day ... perhaps a better
UK▸ comparison to correct for this would be to take the cost of a 5 hour journey - Paddington to Penzance - and include one meal. That comes out at about a pound a mile.
You have, also, allowed for every meal to be a substantial one with wine. Personal habits, of course, but - really - wine with breakfast making up to £125 .... I doubt it!