Woollen bathing costumes were notoriously stretchy, and had a tendency to sag when wet, as they retained water. The trunks are fitted with a drawstring.
This is genuine wartime "utility" clothing, made during the time of clothes rationing in Britain (1941-1949). The label has the official wartime CC41 utility mark.
During the Second World War, there were restrictions on garment design, to minimize waste, and to ensure that resources could be concentrated on providing necessary supplies for the troops, together with a basic standard of clothing for civilians. The CC41 mark showed that these garments conformed with wartime economy standards.
Rationing was also in force - people wanting to buy the utility clothing, would have had to use their clothes ration coupons (as well as paying for the garments). This was to ensure that everyone had an equal chance of buying necessary clothes, and to prevent hoarding and profiteering.
Vintage garment, the best part of a century old, but still clean and in good condition.
It has clearly been looked after, and there are no stains or damage except for a few tiny moth-holes, a one-inch hole in the inner wool lining at the front, and some fraying at the front waistband where the drawstring is tied, where the original "buttonhole stitching" around the hole has given way.
This is shown in the close-up photographs.
Please bear in mind that this item was made in the 1940s, and has suffered some minor moth damage over its years in storage. It is being sold as a collectors' item, or for display purposes.
It is NOT suitable for a trip to your local swimming pool, and would definitely not last long if you tried to wear it!