The message
from Harry Bloomfield contains these words:

I told breeze block is quite suitable for outdoor use, can anyone
confirm this is the case and/or advise on an alternative light weight
building block?

Thermalite do a block called "Trench", which is for underground use.

Personally I wouldn't use aerated concrete blocks anywhere they might
get bashed - they really are very soft. My three year old was merrily
bashing some offcuts the other day and she managed to break up quite a
number of large bits into small bits[1]. They crumble too easily. Go for
dense concrete blocks if it's exposed. Cladding would be sufficient to
protect them.

[1] Did she clear up after her? Did she hell. Gets it from her brother -
and I can't /imagine/ where he gets it from.

--
Skipweasel
Pay no attention to that man behind the curtain.