Well, I've owned a detached for 25 years now so have way of testing anything - but I do know for a fact that the brick-built Semi I had previously had a single brick wall between the two sides - I accidentally knocked a brick out of place while chiselling out for a socket backing box.... Luckily I was on good terms with the old couple next door!
Quick google - these are standard strength aerated concrete blocks; at 100mm & up, they are rated for "Load-bearing single-leaf walls" - so fact not daft.
(There is also a high strength version with twice the load rating).
It does mention thickness & sound attenuation - I'd guess that's part of the building regs, so now thicker walls between semis?
If your blocks are flat, then, as they are around 1/3rd the density of solid concrete, the attenuation (
not structural strength) should be equivalent to ~66mm dry concrete.