In the 1930s, although mass production of car bodies was gradually becoming the norm, it was still customary for the builders of high-class chassis to provide only the chassis; the customer could then choose a body built to their taste by one of the many independent coachbuilders. W O Bentley, who had founded the marque in 1919, had frequently sighed over the fact that so many customers ordered heavy, luxurious bodywork that reduced the performance of his deliberately sporting chassis, and there was no real change for the Derby Bentleys. Nevertheless, Rolls-Royce did insist on inspecting every car once it had been completed by its coachbuilder, and would not provide a guarantee for any it considered might compromise the established Bentley marque values. This prevented any unpleasant excesses - although not every body approved met the highest standards of contemporary taste. By the time of the Derby Bentley, closed bodywork was becoming the norm, and most chassis carried such coachwork when new; drop-head coupé and tourer styles accounted for only about 25 per cent of the bodies built. In fact, the most popular style was the sports saloon, which was not particularly sporting but usually had a ''four-light'' design (with four side windows), whereas the more formal saloons and limousines typically had a six-light design. Even though the general public tended to believe that every coachbuilt body was a bespoke creation, in practice this was far from the case. There certainly were individual designs, but by the time of the 3½-litre Bentley, many coachbuilders had learned how to minimise cost and manufacturing complications by relying on designs they could build in batches.

At the start of a new season, typically in the autumn, they would build a prototype of a new design and display it at the London Motor Show (and, sometimes, elsewhere). When orders began to come in, they might anticipate eventual sales of perhaps ten altogether, and might build them all at the same time. Individual variations could be accommodated so the customer could feel they were buying a bespoke body, but in practice this was the nearest that craftsman-built bodies came to volume production. During the era of the Derby Bentleys, no fewer than 56 different coachbuilders created bodies for chassis that bore the Bentley name when those chassis were new and still in production. The majority were in Britain, but there were also some attractive bodies from coachbuilders on the European continent, especially for customers who lived there. It is also important to remember that body and chassis were not seen as inseparable entities in this period. Several wealthy customers decided to have their cars rebodied after a few years, partly to keep them fresh and fashionable, and partly because (for example) they might have tired of the original saloon and wanted a more frivolous drop-head coupé instead. Though expensive, this was much less costly than buying a completely new car - particularly one that cost as much as a Bentley.

The 3½ Litre, 1933-1937 Once Rolls-Royce had acquired the Bentley business, it was clear it had to get a new Bentley model into production as quickly as possible to capitalise on the goodwill that came with the Bentley name. The simplest and most cost-effective way of doing so was to base the new Bentley on work already being done for a possible new, smaller Rolls-Royce under the code name of Peregrine. This had a lightweight chassis with a wheelbase six inches shorter than the contemporary Rolls-Royce 20/25 model, and was a low-slung type well suited to the sort of sporting bodywork expected of a Bentley. The initial plan to give the Bentley a supercharged version of the Peregrine engine ran into difficulties, and so the Rolls-Royce engineers decided to try a version of the existing six-cylinder 20/25 engine in the Peregrine chassis. The results were immediately satisfying, and Sir Henry Royce gave his approval to proceed with further development towards the end of 1932. Sadly, Royce''s health was already failing, and when he died in 1933 he may never have seen any of the new Bentleys beyond the first prototype.