Reading the national conditions of travel - specifically 9.4 - should the traveller's connection into an afternoon off-peak train be delayed and deliver them to e.g. London Euston after the start of the evening peak, if I've interpreted this correctly, their ticket should be ok for immediate travel in the peak?
Yes, but one caveat:
on the next train service provided by the Train Company with whom you were booked without penalty.'
So if - for example - I had an advance ticket onto a
GWR▸ service from Bath to Plymouth, but missed my connection at Bristol onto their Cardiff to Penzance service, I couldn't drop back onto the next service if it was a Cross Country one.
As a GWR answer, from Paddington I suppose there could be late afternoon issues if you wanted to switch between
TfL» (Elizabeth Line) and GWR. Th e biggest catch would likely by King's Cross, where services could be Great Central, Lumo, Hull Trains and
LNER» and you'll have to catch the correct one of them, some of which are not terribly frequent.