Although it could run in the BTCC, I think the rules mean any points gained couldn't be used towards the constructors championship. Its something to do with meeting s2000 regs.
I'm sure this is the reason Team Dynamics dropped the DC5 for the FN Civic. The small independents could then use the well developed DC5's but not gain constructors championship points.
EDIT: Found this on the BTCC website
"The BTCC is contested primarily by cars complying with the FIA’s Super 2000 technical regulations. S2000 is the same formula as used in the World Touring Car Championship. Teams entering S2000 cars are required to use a model of car that is readily available for purchase in a manufacturer’s showroom across Europe. The old BTC-spec cars, that populated the grid from 2001-06, are still permitted to compete, but are not eligible to win the Drivers’ and Manufacturers’ championship outright. Uniquely, the BTCC remains the only touring car championship in the world that allows cars powered by petrol, diesel, gas or bio-ethanol to compete."