The 3- and 3.5-litre models became favourites for transport of dignitaries, including British Prime Ministers from Harold Wilson to Margaret Thatcher.

[3] The suspension was independent at the front using wishbones and torsion bars and at the rear had a live axle with semi-elliptic leaf springs.

A Mark I-A line, introduced in September 1961, featured a minor restyle with added front quarter windows, intended to "assist the dashboard ventilation".

[3] Under the metal, the 1A featured modifications to the engine mountings and the automatic transmission and hydrosteer variable ratio power steering as an option.

[4] The Mark III was presented at the London Motor Show in October 1965,[3] described at the time as "even more luxuriously trimmed and furnished".

The Borg Warner Type-35 automatic transmission, hydrosteer variable ratio power steering and front Lucas fog lights were now standard.

The greater power of the engine, along with its lower weight, provided improved performance as well as fuel economy.

[8] The exterior was mostly unchanged, apart from bold "3.5 Litre" badging, a pair of fog lights which were added below the headlights, creating a striking four-light array, and the fitting of chrome Rostyle wheels with black painted inserts.

[4] The 3½ Litre saloon variant was a favourite of high-ranking government ministers, and served as Prime Ministerial transport for Harold Wilson, Edward Heath, James Callaghan, and Margaret Thatcher.

It was during Thatcher's eleven-year tenure that the P5 was eventually phased out as a Prime-Ministerial car, in favour of the Jaguar XJ.

Queen Elizabeth II also owned an Arden Green Rover P5B Saloon "JGY 280", which is on display at the Heritage Motor Centre, Gaydon, Warwickshire and was seen in the 18 May 2003 episode of BBC motoring show Top Gear.The Rover P5 is sturdy enough to be a popular choice for banger racing.

In February 1961 the Queen took delivery of her first Rover P5 3 litre Mk 1 which was registered JGY 280 and finished in dark green.

Neither car was obviously different from standard specification, although VUL 4 did carry a discreet identifying lamp at the base of its roof-mounted radio aerial and was illuminated when in use by a member of the Royal family.