The Daimler Fleetline was the second rear-engined double-decker bus chassis to be launched by a UK manufacturer, following Leyland's introduction of the Atlantean in 1958.

This was followed by a code to indicate the engine fitted: D6 (Daimler 6-cylinder, prototypes only); G6 (Gardner 6-cylinder, more often than not this was expanded to the more specific G6LW, G6LX or G6LXB); L6 (Leyland 6-cylinder); C6 (Cummins 6-cylinder).

To counter this, London Transport trialled the AFC (Automated Fare Collection) turnstile entry system on some of the fleet.

[9]: 30  Maintenance costs for rear-engined, front entrance buses were much higher than the older half-cab models due to the inability to separate the body from chassis for modular overhaul.

[15] Withdrawals of the Fleetlines commenced in February 1979, with Leyland Titans and MCW Metrobuses purchased as replacements.

[19][9]: 98–99  However, hundreds of ex-London Fleetlines proved popular second-hand purchases for operators throughout Britain from 1979 and during the 1980s, including the aftermath of deregulation.

In some cases, the special modifications which had been built into the buses to meet London Transport's own specifications were removed at the request of the purchaser, to improve reliability and restore standardisation with other Fleetlines in their fleets.

[29] The Greater Manchester Passenger Transport Executive and its predecessors was another significant operator of Fleetlines outside London, ordering over 500 of the type despite mainly standardising on the Leyland Atlantean.

These were the first double-deck buses designed to take advantage of new legislation allowing for one-person operation of buses in the United Kingdom, with 472 33 feet (10 m) examples subsequently being built on both Fleetline and Leyland Atlantean chassis, most later examples being delivered in the orange and white livery of the SELNEC Passenger Transport Executive.

1 UDH had Northern Counties bodywork with wrap-around windscreens on both decks, similar to that specified by Barton Transport on AEC Regents and a Dennis Loline.

Rotherham Corporation purchased two 33' single deck fleetlines with 45 seat Willowbrook dual purpose bodies.

Mexborough and Swinton Traction Company ordered three similar vehicles with Marshall bodywork for White Rose Express services.

In late 1970, Yorkshire Traction purchased nine 36' Fleetlines with dual door Walter Alexander W type bodywork.

Renumbered 1956 to fit in with the single-decker fleet number sequence, the bus passed to successor West Midlands Travel and is preserved at Wythall Transport Museum.

[22][37] Citybus and Argos Bus, operators of non-franchised routes and private hire services in Hong Kong, also purchased secondhand Fleetlines.