This reference supports my understanding -
http://histclo.com/style/suit/sailor/mil/mil-rn.html -
Another feature of the square rig naval uniform were bell-bottomed trousers. While they have appeared in modern dress as a trendy styles, for the seamen they were very practical garments for sailors. They could be rolled up securely to free the feet and ankles when working the rigging. Not all sources agree with this asertion. [Royal Navy] One American expert writes, "There is no substantive factual reason for their adoption, i.e., easier to roll up or kickoff in the water, but rather appear to be a tailored version of the pantaloon, designed for a bit of flair which set the sailor apart from his civilian counterpart." [Cruse] The sailor, like all other items in his kit, kept his trousers neatly folded ready for use in a kit bag. They were folded inside out to avoid fluff on the outer surface and to prevent 'shine' as a result of ironing. The trousers were folded horizontally at about a hand's width and taped into a rectangular 'block'. When worn, this produced inverted vertical creases down the side of the sailor's leg and five or seven, depending on the height of the wearer, horizontal creases down the leg. In time these were accepted as the proper uniform look. Thus these creases were pressed firmly into place from the early years of the 20th century. Once sail power vanished in the late 19th century, bell bottoms no longer had any practical purpose. Since World War I, sailors wore bell bottoms primarily tradition. The Royal Navy replaced them with flared trousers in 1977.
As a personal aside ratings who joined on the 19th Sept 1978 were the first entry to not receive any bell bottoms at all - the entry before having received bellbottoms as a No 2 (working) uniform
