i use ronseal varnish's both satin & matt there not water based
Actually Ronseal are now marketing water based varnishes which confuses things, especially as the original polyurethane solvent versions are now less easy to get hold of!
The polyurethane solvent varnishes have the advantage that they can be applied over just about everything without reacting and can be brushed on or thinned down for airbrush use. It's certainly worth investing in the matt and satin versions of these if you can find them, preferably the interior versions as the exterior versions have UV filters which give a slightly yellow tint which is noticeable over light colours.
As well as Ronseal, you can get similar products from Blackfriars, Rustins and even Wilko.
Buy now before they go!
Another tip. If you are in the market for white or coloured exterior paint then ignore the stuff in the DiY stores and go to a marine chandlers and buy something like International Toplac yacht enamel. It is more expensive but it is intended for painting boats and will last much longer on domestic applications inside and out. Goes on well too.
Colin