Don't forget the hallowed BR combination - a BLT, McEwans Export and 20 Bensons you could actually smoke on the Train never mind the platform.
Even if privatisation hadn't happened, I'm sure that BR would still have phased out smoking accommodation on trains (as the anti-smoking law would still have come in), but it would probably have been abolished on medium distance InterCity routes first (i.e. the Midland and Great Eastern main lines, and maybe Euston-West Midlands and King's Cross-Leeds) and then on the longest-distance routes.
As it was, for a few years you could smoke on Midland Main Line and Liverpool Street-Norwich trains (with a journey time of no more than 2 and a half hours) but not on Great Western (with journeys of up to 5 hours) or Virgin CrossCountry (up to 12 hours West Country to Scotland).