Sometimes called "the poor man's Rolls Royce", the P5 was extremely popular with United Kingdom Prime Minister and government officials of its day. Even the Queen is said to have favoured driving her P5.
The P5 appeared in September 1958, badged as the "3-litre". It was powered by a 2,995 cc (2.995 L; 182.8 cu in) engine. This straight-6 F-head engine used an overhead intake valve and side exhaust valve, an unusual arrangement inherited from the Rover P4. In this form, output of 115 bhp (86 kW; 117 PS) was claimed. An automatic transmission, overdrive on the manual, and Burman power steering were optional with overdrive becoming standard from May 1960.
Stopping power came originally from a Girling brake system that employed 11-inch (280 mm) drums all round, but this was a heavy car and by the time of the London Motor Show in October 1959 Girling front-wheel power discs brakes had appeared on the front wheels.
A Mark I-A line, introduced in September 1961, featured a minor restyle with added front quarter windows, intended to "assist the dashboard ventilation". Under the metal, the 1A featured modifications to the engine mountings and the automatic transmission and hydrosteer variable ratio power steering as an option.
By 1962, when production of the original Mark I series ended, 20,963 had been produced.
An automatic version tested by The Motor magazine in 1960 had a top speed of 95.0 mph (152.9 km/h) and could accelerate from 0–60 mph (97 km/h) in 17.1 seconds. A fuel consumption of 20.5 miles per imperial gallon (13.8 L/100 km; 17.1 mpg-US) was recorded. The test car cost £1864 including taxes.
The Mark II version of the P5 was introduced in 1962. It featured more power (129 hp/96 kW) from the same 3.0 L engine and an improved suspension, while dropping the glass wind deflectors from the top of the window openings which also, on the front doors, now featured "quarterlight" windows (Quarter glass in US English).
The most notable addition to the range was the option of the Coupé body style launched in autumn 1962. Unlike most coupés, which tend to be two-door versions of four-door saloons, this retained the four doors and was of the same width and length as the saloon, but featured a roofline lowered by two and a half inches (6 cm) along with thinner b-pillars, giving it the look of a hardtop. Hydrosteer was standard on the Coupe and optional on the Saloon.
Production of the Mark II ended in 1965, by which time 5,482 coupés and 15,676 saloons had been produced.
The Mark III was presented at the London Motor Show in October 1965, described at the time as "even more luxuriously trimmed and furnished". It was again available in two 4-door body styles, coupé and saloon. The Mark III used the same engine as its predecessor, but it now produced 134 hp (99 kW). Externally it could be distinguished by the full-length trim strip along the body and Mark III badging; internally it replaced the rear bench seat with two individually moulded rear seats, making it more comfortable to ride in for four occupants but less so for five.
A total of 3919 saloons and 2501 coupés had been sold by the time production ended in 1967.
The final iteration of the P5 appeared in September 1967. Now powered by the 3,528 cc (3.528 L; 215.3 cu in) Rover V8 engine also used in the 3500, the car was badged as the "3.5 Litre", and commonly known as the 3½ Litre. The final letter in the "P5B" model name came from Buick, the engine's originator. Rover did not have the budget or time to develop such engines, hence they chose to redevelop the lightweight aluminium concept Buick could not make successful. They made it considerably stronger, which added some weight but still maintained the engine's light and compact features. The Borg Warner Type-35 automatic transmission, hydrosteer variable ratio power steering and front Lucas fog lights were now standard.
Output of 160 bhp / 119 kW was claimed along with improved torque. When compared to its predecessor, the aluminium engine enabled the car to offer improved performance and fuel economy resulting both from the greater power and the lesser weight of the power unit.
The exterior was mostly unchanged, apart from bold '3.5 Litre' badging, a pair of fog lights which were added below the head lights, creating a striking 4 light array, and the fitting of chrome Rostyle wheels with black painted inserts. The P5B existed as both the 4-door coupe and saloon body style until end of production. Production ended in 1973, by when 9099 coupés and 11,501 saloons had been built.
One of the curiosities of the P5B is that the trim of the nearside front wing is a different length to that of the offside.
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. As testament to their suitability, the last batch of P5Bs to roll off the Rover line in June 1973 were purchased by the British government and placed in storage, to be released for government use as required: subsequently registered relatively new looking P5s were therefore still familiar sights in Westminster for more than a decade after production had ended.
When Margaret Thatcher entered Downing Street in 1979 after her election victory, she was driven in a 1972 model. 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 owns 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.