I did my conservatory as follows
Wash down, degrease and sand. Wash again
2 coats zinser primer. The one specifically for upvc. I got it from Johnstons and got them to put a dark tint in to get nearer the top coat colour and also I was painting dark over the upvc white which is easier to see than white over white
2 coats top coat, Johnston acrylic as advised by shop guy.
I’m very pleased, after 4 years it’s looking great and has transformed the conservatory for very little cost.
Things to be aware of – any silicon on the upvc frames will throw paint off so you’ll have to remove it first, paint then re silicon
I used a brush but now I would use a small foam roller.