I've just got a quote from Miller Pattison (via British Gas) to do cavity
wall insulation in a 3-bed chalet bungalow (where about 25-35% of it
already has some because it's a new extension).

They have quoted £250 basically, plus £45 to fit a vent in the sitting room
(required apparently because there is a fireplace). I think I am getting
something fairly minor like £25 off from British Gas.

I'm sure I heard that a building like this could be done for something like
£125 with the grants available. I know this varies from region to region,
but does anyone have any general advice on how to find out if this is the
best I can get, or does anyone in Wilts have any specific advice on grants?

By the way, does it seem odd to anyone else to go to all that trouble
insulating a house and then punch a dirty great air vent in one room? He
hinted that many people gaffer-tape them up when he's left.