Interesting! I checked out what the RNLI had to say at https://rnli.org/safety/lifejackets and that page only mentions lifejackets along with gas.
However, if you "Download our lifejackets and buoyancy aids guide as a PDF (3.48MB)" at https://rnli.org/-/media/rnli/downloads/1983319_choose_it_we... you'll read "Children’s lifejackets may rely on foam, air and foam, or CO2 only to provide buoyancy" and "Air and foam or CO2 lifejackets meet the requirements of a level 150 lifejacket and are suitable for offshore use. Normally, foam lifejackets provide level 100 buoyancy
and are suitable for inshore use."
A further search of the RNLI site finds https://rnli.org/magazine/magazine-featured-list/2018/june/t... with "The foam-based Beaufort lifejacket [of the 1970s] upped the buoyancy level, allowing a crew member to also support the person being rescued." but by the 1990s "The bulkier gear of all-weather lifeboat crews meant they needed a more compact lifejacket, which inflated automatically on hitting the water using a built-in gas canister."
Since I learned my small watercraft skills in the warm waters of Florida, instead of chilly UK, I can see how that would make a difference.
However, if you "Download our lifejackets and buoyancy aids guide as a PDF (3.48MB)" at https://rnli.org/-/media/rnli/downloads/1983319_choose_it_we... you'll read "Children’s lifejackets may rely on foam, air and foam, or CO2 only to provide buoyancy" and "Air and foam or CO2 lifejackets meet the requirements of a level 150 lifejacket and are suitable for offshore use. Normally, foam lifejackets provide level 100 buoyancy and are suitable for inshore use."
A further search of the RNLI site finds https://rnli.org/magazine/magazine-featured-list/2018/june/t... with "The foam-based Beaufort lifejacket [of the 1970s] upped the buoyancy level, allowing a crew member to also support the person being rescued." but by the 1990s "The bulkier gear of all-weather lifeboat crews meant they needed a more compact lifejacket, which inflated automatically on hitting the water using a built-in gas canister."
Since I learned my small watercraft skills in the warm waters of Florida, instead of chilly UK, I can see how that would make a difference.