Don't know which fixed it but I used two unusual products recently:
Bathroom limescale and tile cleaner
Lynx antiperspirant.

Seem to have done the trick!

Sea drops, available in any dive shop on this side of the pond, works well.
If you can't buy them in  your local shop, order some from diversdirect.com.
http://www.diversdirect.com/scripts/ecatalogisapi.dll/ItemSearch?Template=999000
0041000999&searchn=0&maxresults=12&searchinput=sea%20drops.

You may have trouble with finding a shipping link to the UK.  They will ship
to you, but last time somebody over there needed something from here, there
was no link on the order site.  You may have to email them about it.  If all
else fails, send me a private email (drop the 2 from the address used to
send this message) and I'll run over and pick a few bottles up and send them
to you.  Mail to there bumps the cost up a bit, but if you need them.  I've
done similar things for several UKRS members.

There's something else you can do to help the problem.  Quit breathing
through your nose.  Those that have severe problems with mask fogging are
almost always breathing out through their nose just enough to increase the
moisture in the air trapped in the mask, moisture that condenses on the
lens.  Break that habit, and the problem will diminish.  The less moisture
to condense, the less fog can form.

You can get away with breathing out through your nose in warm water, where
condensation on the lens is not as much of a problem, but the colder the
water, the more likely you are to have a problem.  I sometimes have the same
problem.  When I do, I spend some time underwater with no mask, either
breathing through a snorkel or from a tank.  Either way will help break the
habit in short order.

Lee

I soak my mask in "Simple Green" AND clean it with toothpaste! It's not just
the lens that needs to be cleaned but also all the silicone inside the mask,
make sure you clean under the seal. The chemicals on the silicone will foul
the glass and cause fogging. I do this when the mask is new and once or
twice a year also. I use defog before each dive because it's cheap insurance
against looking through a fogging mask. If you don't clean the mask first,
the defog or spit will be useless.

Al
Bottoms Up Divers

I've been using Charlies Soap spray,use once every 6 months works for me.
Cleans the gear also.
Safe diving all,Paul.

I would not use toothpaste .. that is an abrasive and scratches teh
lens ... and no way I want to do that on a new expensive mask.

There is a company in UK that makes a new mask Preparation product ...
a couple of drops removes all traces of silicon mould release (which
is what causes much of fogging)

I also use their anti-fog which I find brilliant, I did try Typhoon
anti-fog, which was as useful as a chocolate teapot.

NMP   is on http://www.salclear.com/nmp.htm

Salclear Ultra  http://www.salclear.com/ultra.htm

I found  out about this company after buying their Dive e-drops at the
Dive show -

I think they sell a 'Diver pack' which has all 3 items in one kit.