The crest was the first addition to the Shield borne on top of a Helm. It was during the reign of Edward III that the crest began to be widely used in English heraldry. The first representation of a royal crest was in Edward's third Great Seal, which showed a Helm above the arms, and thereon a gold Lion statant guardant standing upon a Chapeau, red and turned up ermine.
This design (aquiring a royal crown of its own on its head) has pretty much remained the Crest of England (and subsequently the United Kingdom) ever since. Some may query why the Lion in the Crest isn't equally passant as those on the Shield. Why it is statant or standing on all four paws without the one paw raised, further to a contention that this pose is more widespread on Crests than on Shields, I am not aware.
The exact form of Crown used in the crest varied over time. Until the reign of Henry VI it was usually shown as an open Circlet adorned with fleurs-de-lys or stylised leaves. On Henry's first seal for foreign affairs the design was altered with the Circlet decorated by alternating Crosses formy and Fleurs-de-Lys. The double-arched Crown was introduced by Henry VII. Since the late 17th century, with the Restoration, the Crown has consisted of a jewelled Circlet, above which are alternating Crosses formy and Fleurs-de-Lys. From this spring two Arches decorated with pearls, and at their intersection an Orb surmounted by a Cross formy. A Cap of crimson velvet is shown within the Crown, with the Cap's ermine lining appearing at the base of the crown in lieu of a Torse. The shape of the arches of the Crown has been represented differently at different times, and can help to date a depiction of the crest. As we have seen previously, this can generally be either a Tudor Crown or one more representative of St Edward's Crown as at present.
The Helm on which the crest was borne was originally a simple design, sometimes with embellishments. In the reign of Elizabeth I a gold Helm with a barred Visor, facing the viewer, was introduced. The decorative Mantling was originally of red cloth lined with ermine, but was altered to cloth of gold lined ermine by Elizabeth and has stayed so to the present day.
The above photo shows the work of renowned heraldic scultor Ian G. Brennan, who, In 1989, was officially appointed ‘Sculptor to the Most Noble Order of the Garter and the Most Honourable Order of the Bath’. The central Crest is that of HRH The Duke of Cambridge which is based on the Sovereign's Crest. (www.heraldicsculptor.com)