The purpose of this Royal Air Force survival suit was to allow those members of a ditched aircrew who got into a lifeboat to have a combination suit/sleeping bag with a hood in which they could rest whilst other members of the crew sailed the lifeboat.
Although the suit bears the 22C vocabulary coding, they are not actually flying clothing. Air Publication 4380 Data Book on Safety and Survival Equipment and Flying Clothing has them catalogued as Suit, RAF, Inner, Ditched Aircrew, Non-Working Pattern.
This object is not on display at the National Air and Space Museum. It is either on loan or in storage.