(or Coach-and-six). It is said one may drive a coach-and-four through an Act of Parliament, i.e. lawyers can always find for their clients some loophole of escape.
“It is easy to drive a coach-and-four through wills, and settlements, and legal things.” —H. R. Haggard.
“[Rice] was often heard to say that he would drive a coach and six horses through the Act of Settlement.” —Welwood.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894
More on Coach-and-four from Infoplease: