The Wicked Lady (1945), directed by Leslie Arliss.
This is a pure example of that distinguished literary genre, the Bodice Ripper. In 1683, unscrupulous Margaret Lockwood just wants to have fun. And her best friend's fiancé, a big house and lots of money. And her own way in everything. Bored with her marriage she sneaks out at night and becomes a masked highwayman, holding up coaches with a gun. She links up with another bandit working that stretch of road, the suave and dangerous James Mason, and they become partners in crime. After a night of stand-and-deliver, they retire to a room at the highwaymen's favorite inn for private unmasking and carousing. What could go wrong?
There is more story than that, but such is the exciting part apart from bawdy banter and assorted hanging, poisoning and smothering. The film is based on a novel suggested by a real legend.
I learned of this film from George MacDonald Fraser's The Hollywood History of the World:
quote
...it fulfilled the popular notion of the Restoration as a time of flopping wigs and bulging bosoms (which it was) when gallants and wenches rioted in four-posters and discarded heaps of fashionable clothing. [...] a considerable success, it was rated the height of daring and vulgarity at the time, with Miss Lockwood being compared to Jane Russell, and cleavages having to be discreetly re-shot for the American market.
We do indeed have ample expanses of heaving bosoms and aggressive décolletage, but I don't know which bits had to be adjusted for the US censors. It is a product of the long-defunct Gainsborough Studios which by this time specialized in "a series of morally ambivalent costume melodramas for the domestic market mostly based on recent popular books by female novelists."
Available only in PAL DVD. (Later: Criterion had this in a boxed set of three films).