I'm not too keen on painting the entire model by brush due to the possibility of putting on too thick a coat (one of the reasons I used a spray paint to put the base coat on), but looking at the cost of a spray can of gloss varnish (£5+) and considering I have a bottle of Future (albeit from 1997) perhaps brushing it on the whole model might be the best route.
Just need a larger brush, I've ordered an Italeri size 6 brush from an ebay seller today as I currently only have a couple of Game Workshop detail brushes, hopefully a size 6 will be large enough.