I think its fair to say WSR have a huge amount of success in the BTCC running Ford, Honda, MG and now BMW but like has been said does that make you the most successful non works BMW team ? WCR have a better track record and more titles. Some time I think BTCC teams bask in the BTCC's former glory too much.
WSR did launch th career of one Ayrton Senna though so they might have a right to boast, just not about their BMW achivements