text: By the late 1920s, a more convenient version of the temporary roof was often being used where a solid metal panel would slide into a slot at the top of the passenger compartment, sometimes called a de Ville extension. By the early 1930s, cars were being constructed in the Sedan style comprising a metal one-piece roof without the gap above the driver's cabin. To provide a similar facility to the earlier Coup de Ville configurations, sliding cloth or metal panels recognisable as the modern sunroof were regularly fitted to Bentley and Rolls-Royce models built by coach builders such as Barker, Gurney Nutting or Park Ward. In these cars, the continuous roofline, between the windscreen and passenger compartment, was unbroken and so, unlike the Coup de Ville, a coverable opening had to be let into the roof panel itself.
  While at first the purpose may still have been to expose the chauffeur, Bentley cars in particular were increasingly sold for owners to drive themselves. Indeed, some models were provided with a sliding panel for the front seats even though the vehicle had just two-seats. Early "Derby" Bentley hard-top models were therefore frequently equipped with sliding sunroof panels, possibly more often than not. The purpose of the sliding panels thus changed from uncovering the chauffeur to allowing the owner to better enjoy their surroundings on fine weather days.