Airfix painting problem?

Hi, I am having problems with painting my Hawker Huricane Spitfire and Me 109 I put on a coatn of white all my paints are humbrol ones and it dried and they all went patchy so i thought maybee i should do a second coat second was streaky and then thurd was to think uneven terrible it looked like house paint when it dried. Any ideas were I went rong?