I'm also surprised that insulated shutters aren't more used or talked about. They seem the obvious answer to the problem of utilising daytime light and solar heat but mitigating the downside of nightime heat losses. Also useful for keeping buildings cool in summer.

The topic has long been raised on the forum by several people including the ususal suspects. It is actually become more relevant for two reasons. Firstly, all enhancement of insulation produces diminishing returns, and in the case of walls and ceilings losses are easily reduced to minimal levels. That leaves windows, even with DG, as the major escape route for heat. Secondly, higher building regs on overall thermal losses are forcing people to greatly reduce window sizes to meet the limits imposed. The resulting 'houses' are not quite caves, but certainly heading towards dark medieval houses (where cost of glass was the motivation for small windows), with greater lighting requirements all year - ignored by regulators! My understanding also is that calculations make no allowance for use of either shutters or curtains: typical crazy government.

Those who have looked at the problem, including myself, have not come up with a good design. There are 3 challenges: tightness of fit, insulation property, and concealment when open. Reasonably tight-fitting traditional internal wood shutters do quite a good job, as wood is quite a good insulator, and they fold back into shutter boxes to form an attractive feature when not in use. The fact that overnight even DG gets mass condensation behind the closed shutters proves the point. With heavy curtains added, the effect must be substantial.

Obviously this is only a saving at night, but at UK latitudes and climate that is a very substantial factor, albeit it requires a commitment by occupiers to open and close each day.

External shutters are theoretically desirable, but I see little likelihood of people shutting them nightly. There are also obvious aesthetic and practical problems. Concealed and automated external 'security type' insulated roller shutters could be incorporated in new-build at a price.

So, as it happens I DO have loads of external lovered shutters covering both doors and windows on 2 floors (with wraparound balconies), and even if shutting them might be a bind for us I am sure we could add it to my 10 year old's Pocket money agreement. So, have just paid for the info and I'll let everyone know what I think. A bit skeptical because there are no photos or descriptuions of what the finished item looks like and since I now live in Italy (where form follows exactly the way it has always been or it is "Brute!' (ugly)) I woonder if I have just wasted 3pounds50.

Meanwhile, given I will insulate my roof, draught proof all my doors and windows and leave my solid stone walls alone for now (oh and the "up to 40% savings" claim), is it better to insulate the shutters or double glaze the windows ('better' as in measured strictly by fuel savings fo heating)?

That sounds ideal. Maybe with rubber seals around the edges of some suitable profile, so that they are relatively well sealed when closed - http://www.tym.co.uk/ do lots but there are plenty of other suppliers.