With the introduction of Diesel Multiple Units gathering pace during the 1960s, much of the Mk1 non-gangway stock was phased out of traffic, but for some of the vehicles new uses were found, especially in freight flows and, later, as Departmental vehicles.

With the introduction of Freightliner trains, British Rail and the Train Drivers’ Union, ASLEF (The Associated Society of Locomotive Engineers and Firemen), were unable to come to an agreement over where Guards should be housed in these new fully fitted trains. Initially, containers were converted into ‘Caboose’ style accommodation but with the ride and safety severely compromised, it was decided to convert a number of redundant Mk1 Brake vehicles into Freightliner Guards’ Vans as a temporary measure until a more permanent solution could be found.
The majority of these vehicles were converted from Mk1 non-gangway Brake Seconds, with 43 ex-Midland, Eastern and Scottish coaches being converted at Derby and Swindon works between June 1966 and October 1967, entering service on Freightliner flows in a plain grey livery.

Once BR and ASLEF had reached an agreement for Guards to ride in the rear cab of the hauling locomotives, the Brake vans were once again surplus to requirements, with just seven vehicles being pressed into service as Departmental vans: DB 963904, 963906, 963925 and 963947 as Crane Runners and ADB 963943, 963952 and 963953 as BTU Tool Vans. ADB 963952 started life as Sc43326, one of the 1955 York built Brake Thirds built to Lot 30057 and once retired from the Scottish Region, was converted into a Freightliner Brake Van at Swindon in September 1967. Conversion to a BTU Tool Van took place at Doncaster in 1980 and the vehicle stayed in service until June 1988, when fire damage rendered the coach unusable and it was eventually cut up at Temple Mill Yard in June 1992.