The development of the Plus 8 was led by Maurice Owen, an engineer taken on specifically for the role. The Plus 8 prototype was based on a modified chassis from the +4, altered to accept the Rover alloy block 215 cu in (3.5 l) V8. The chassis was developed in stages to accommodate gearbox changes in 1973 and 1976, the body widened in 1976 to accommodate the widened chassis and the wings widened to accommodate larger tyres to handle the increasing power and trend for lower profile and wider tyres.
At the end of 1983, the company offered an EFI version using a Bosch L-Jetronic based system. With the added power (204 bhp (152 kW; 207 PS)) and low weight, the Plus 8 was, according to the magazine road tests of the day, able to best a Porsche up to 90 mph (140 km/h). In 1990 a 3.9 L version of the engine was fitted and that used the Lucas fuel injection.
To mark the 35th year of production of its Plus 8, MMC released a commemorative 'Anniversary Edition' in 2003.
Following the discontinuation of the Rover V8, production of Plus 8 ended in 2004. A revised Plus 8, powered by a 4.8-liter BMW V8 engine, was introduced in 2012.