Thanks Hugh.
A bit frustrated at the moment. I spent around two hours last night, attempting to get a decent matt clear coat on the prop ( and some other "test" surfaces) without any luck. I used my new bottle of Vallejo, a brand which has always worked fine whether brushed or airbrushed, and again it dried gloss. I then tried two other brands, one of which dried semi gloss, and other, although it dried matt, had a chalky appearance.
I'm thinking that the new bottle of Vallejo, being 500ml as opposed to my earlier 60ml bottle, has settled in storage since I bought it some time ago.
I did give it a vigorous shake, and poured a little into a plastic shot glass and gave that a good stir, but I think it needs a really good stir, either in the bottle ( a bit difficult), or maybe decant a decent amount, stir that, and pour some into the smaller bottle.
I'll try this, but rather than get bogged down with what I hope is a minor problem, I'll leave this for now and move on to the decals, which i hope to start this evening.