The multi-class Group A regulations that had governed the BTCC through the late 1980s were formally replaced by Super Touring rules that had evolved from Group A's Division II category. Super Touring cars were required to use 2.0-litre engines, production-based bodywork, and front-wheel drive, creating a formula intended to be both commercially relevant and technically demanding. Group A machinery was still technically permitted in 1991 but was restricted to bring it down to Super Touring performance levels.
BMW and Vauxhall held a significant advantage entering 1991, having run Super Touring cars during the transitional 1990 season and therefore gaining a year of development ahead of rivals. BMW fielded the largest factory presence, with the official Prodrive team running two cars alongside the semi-factory Vic Lee Motorsport operation fielding four — a total numerical dominance that would influence the season's balance of power.
Vauxhall entered two cars, as did Toyota, while Ford fielded just a single entry for Robb Gravett's Trakstar team. Nissan missed the start of the season before joining mid-year with a single Primera for Keith O'Dor, entered by Janspeed, and later added former Formula One driver Julian Bailey. Mitsubishi returned through John McGuire Racing with a single entry for Mark Hales, beginning the year with the Lancer GTI before switching to the Galant mid-season.
The privateer field consisted primarily of BMW M3s, supplemented by occasional Ford Sierra entries. Andy Middlehurst was among the most notable of the independent runners. Brief appearances from Rover and Peugeot were made by privateer entries, while mooted participation from Audi, Honda, Renault, and Lancia never materialised. A landmark moment came at the seventh meeting at Silverstone, where future three-time BTCC champion Matt Neal made his series debut in a Pyramid Motorsport-run BMW M3, finishing thirteenth out of seventeen classified finishers.
The title fight narrowed to a straight contest between Will Hoy and John Cleland across the course of the season. Hoy won the opening two races and maintained consistent scoring, building a position from which he could claim the title at the penultimate round at Thruxton — provided he secured a strong enough result.
At Thruxton, Hoy led the race with the help of BMW team tactics, but was controversially spun by works BMW driver Jonathan Palmer. Hoy dropped down the order and later retired following contact with Cleland himself. Cleland finished eighth with a damaged car, leaving the championship undecided heading into the final round. There, Hoy was able to finish ahead of Cleland and claim the first Super Touring championship, a title that would take on historic significance as the Super Touring era subsequently defined British motorsport through the 1990s.
Andy Rouse finished third for Toyota in the standings, while Steve Soper ended fourth overall despite missing several rounds due to commitments in the German DTM championship.
One race during the season at Silverstone was stopped after ten laps due to heavy rain and not restarted, with no points awarded. Tim Harvey was docked 48 points in round three for noise regulation violations, a penalty that significantly affected his championship standing.
The 1991 season launched the Super Touring era that would make the BTCC one of the most watched domestic motorsport series in the world through the 1990s. The formula attracted major manufacturers — BMW, Vauxhall, Ford, Renault, Honda, Peugeot, Nissan, Volvo, Alfa Romeo, and others — turning the championship into a genuine battleground for automotive marketing during the decade. The 1991 season's competitive intensity, the Hoy-Cleland rivalry, and the drama at Thruxton established the standard for what the Super Touring BTCC would deliver annually for the following decade.