Hi Carolanne,

Plasterboard is only frowned upon when used for 'dot and dab' ie stuck to the wall with blobs of adhesive. This is because air can circulate behind leading to heat loss throgh other gaps in masonry, flooring and ceiling junctions etc. This is not always the case and your conservatory may be reasonably airtight behind the plasterboard. I would not worry about this in a conservatory anyway as most of the heatlost will be through the glazed areas. You probably won't be heating it anyway?

As far as plastering in concerned, it will give you a better finish to paint over and will help with reducing heat lost through air leakage, although it is common these days for people to just tape the joints and then paint over. I prefer to plaster myself but it all depends how well the boarding has been done and whether you are happy with how flat it is now.

Plaster gives next to nothing in terms of insulation. Hope this helps