Can anyone give some historical details of when/where etc. houses
started to be built with cavities in party walls in British
terrace/semi houses ?

Also, is a modern party wall much more sound proofing that the 9"
brick ?

If so, this could be a factor in future home purchases. Unfortunately
you cannot tell how well the wall has actually been built. Some of the
30s walls are very dodgy when you remove the plaster, since they were
never intented to be seen.

I moved from a house with a quiet old person next door to a house with
a family next door, both 1930s 9" party wall. It made me wonder how
much noise we used to make for the old lady in the previous house !
Then banging on the stairs next to the party wall is most noticable,
especially children running up and down.

I know in the 1930s people had less electronic noise, but surely they
spoke just as loudly.

Thanks,
Simon.