[3] Its prototype, the one-off P61 introduced in 1963, pioneered many of BRM's monocoque elements, but used a tubular subframe for its rear engine mounting.

Shifting the inlets to the outer edges of the car allowed the engine to ingest cooler, denser air, boosting the motor's power output.

[3] The engine's internals remained almost unaltered from the Peter Berthon-designed unit which was installed in the V8 version of the P57, the BRM P578, with which Graham Hill had won the World Championship in 1962.

BRM had experimented with a four-valve-per-cylinder version of the engine, but this was abandoned in favour of the tried and trusted, oversquare (68.5 x 50.8 mm), fuel-injected, two-valve, quad-cam configuration.

[1] In 1966 the Formula One upper engine size limit was raised from 1.5 to 3.0 litres, and the 1.9-litre Tasman unit was pressed into service for the World Championship as well.

For the P261's 1967 trip to the Antipodes the engine capacity was stretched yet further, providing the ultimate 2,136 cc (130.3 cu in) version, which also saw service in a few Formula One races later in the year.

This switch was initially made to accommodate the extra cam-cover space needed to employ the 32-valve motor, but though that unit was shelved the suspension geometry was retained.

[3] At the front, the coil spring and damper units were retained within the monocoque skin, resulting in a clean, aerodynamic profile around the car's nose-cone.

The car immediately showed its promise, as Hill took second place in qualifying, beaten only by newly crowned World Champion Jim Clark's Lotus 25.

Despite the rather interim nature of its engine and chassis configuration, on its World Championship debut at the 1964 Monaco Grand Prix the BRM P261 had the best of starts.

Hill bounced back to win in the United States, but finished out of the points at the season finale in Mexico following a collision with Bandini.

Hill again won in Monaco and the USA, while Stewart eventually took a closely contested Italian Grand Prix, his first ever World Championship race win in only his first Formula One season, wiping out memories of the previous year's humiliation at Monza.

Following the end of the 1965 World Championship season, BRM fitted two of their chassis with the enlarged, 1.9-litre version of the V8 engine, and shipped them to Australia and New Zealand to compete in the Tasman Series.

Hill and Stewart accompanied them, along with substitute driver Richard Attwood, and immediately set about dominating the championship, despite the P261 giving away over half a litre to the older Climax-engined cars.

Team Chamaco Collect entered American Bob Bondurant in five races, and British-born South African Vic Wilson in one.

Parnell continued to run a 2.1-litre P261 for Chris Irwin and Piers Courage during the subsequent 1967 Formula One season, and Bernard White ran another for David Hobbs at the British and Canadian Grands Prix.

But with the widespread availability of the Cosworth DFV 3-litre V8 in the 1968 Formula One season there was little reason for running with an outclassed and underpowered old chassis in Europe beyond the end of 1967.

Australian driver Frank Gardner attempted to qualify the V12 engined car for the 1968 Italian Grand Prix, but his time was too slow.