The order of introduction was ECML in 1971, WCML in 1972 and WR (Bristol/S.Wales) in 1973. When both the HST and LMR Mk3 sets appeared, they started to work on other services.
And for completeness, December 1972 for CIÉ and exactly the same occurred there - once the first Mk3s appeared in July 1984, the Mk2Ds began to migrate to other workings eventually covering routes that had previously only seen "orthodox stock".
Was there much mixed working with early Mk2's and air con ones mixed in a set?
Not uncommon to see the odd PV Mk2 in an otherwise air-con set making up the seating capacity when presumably the booked air-con vehicle was out for maintenance and no spare available or sometimes there weren't actually enough of a specific type, so a PV one was used anyway.
The WR had no air-con Mk2 brakes originally, so sets had either a Mk2C BSO or a Mk1 BG.
Mixed sets were more common on CrossCountry workings in the early/mid-80s it seemed, particularly with the second class vehicles.
Though, the so-called "Jumbo" sets the WR made up for the busiest Paddington/West Country workings as capacity busters were also highly mixed PV & air-con Mk2s.
The Mk2 push-pull sets on ScotRail could also feature the odd PV Mk2 and in the latter years one or two sets were very mixed.
dont think any Mk2 air con catering vehicles were built.
As new, only for CIÉ in Ireland.