I am not quite old enough to remember much of these years, having been born in 1959. But one memory I do have shows a fascinating (to me) perception of the traveling public at that time.There were, of course, other London trains which were steam worked due to diesel failures and unavailability.
The occasion was my very first day out to London with my Auntie and her friend - it would have been 1963 or '64. Amidst huge excitement, we took one of the new "diesel trains" from Temple Meads to Paddington. At the end of our day out, we arrived back at Paddington, whereupon my Aunt exclaimed "Oh no - our train has a steam engine! It's going to be a slow and dirty ride home." I plainly recall the general moans of dissatisfaction from many other passengers too.
I have since seen much publicity from the era and it is apparent that the Western Region (and probably all others) committed substantial marketing resource to the promotion of their new diesel loco fleets, as to their being faster, cleaner - and "more reliable" (sic - during the early days at least!)
However, what is plain from this small memory is that by 1963/64, the traveling public seem to have been well and truly "educated" into a positive appreciation of the new diesels and a healthy dislike of "dirty old steam engines". Hardly surprising considering the level of investment that went on during the modernisation period, I suppose.
Strange how perceptions change over the years - most people would be queuing up for a trip to Paddington behind a Castle or a King nowadays. But in the early 60s and set against Harold Wilson's "White Heat of Technology" era, slum clearance and the then new development of what we now call 1960s planning blight, most of the general public wanted the past firmly put "in the past" and welcomed the new diesels as part of the collective "bright new future".
That's my take on it anyhow