OK, but remember the settlement is likely to be due to shrinking clay
(North
London) so if you build it straight off the oversite it will probably
settle
(relative to the main house walls) again in time. Ideally it needs a
decent
foundation, to the same depth as the main walls. Also, make sure you
leave some
holes in the wall to allow air to circulate.

Peter

I thought this method of house construction put everything (from outer walls
inwards) onto one large concrete slab, rather than have the main walls on
separate foundations? That's certainly what it looks like as far as I can
see. Either way some further settlement seems inevitable but at the current
rate of less than 5mm per decade I think I can live with it.