The Alfa 155 dominated 1994, when the Volvo Estate raced. They used a homologation special (Silverstone Edition) to allow them to use an adjustable front spoiler, and a raised rear wing, apparently several of the parts weren't installed, just put in the boot. 🤣 Although according to Gabriele Tarquini it was the differential that made the biggest difference over the competition. (Interview with 1994 BTCC champion, Gabriele Tarquini.)
The following season aerodynamic aids were permitted, which the estate couldn't use, something like the rear wing wasn't allowed to be visible from the front of the car, It wasn't banned, it was just no longer able to be competitive under the new regulations.