Guy King wrote:
The message
from The Natural Philosopher contains these words:

Water runs down the inside of your exterior brick/stonework during
heavy rain...

It bloody well should NOT. If it is you have a serious problem.

Though provision is made here
http://tinyurl.com/ozshd
on page 37ish for not filling cavities right up to the oustide leaf in
many parts of the country because of the risk of water penetration.

I thinkthat refers to filling the width of the cavity rather than the
height, IE putting a 35mm insulation board inside a 70mm cavity, keeping it
away from outer leaf for this very reason.

Filling the cavity after construction (the method discussed in this thread)
is covered on poage 34:

c) Other insulating materials inserted into
the cavity after the wall has been constructed
should have certification from an appropriate
body and be installed in accordance with the
appropriate installations code. The suitability of
the wall for filling is to be assessed before the
work is carried out and the person undertaking
the work should operate under an Approved
Installer Scheme that includes an assessment
of capability.
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No accredited or approved company will fill a house built with undressed
stone in the cavity, nor would it be garuanteed if they did.