Thanks for your thoughts Robbie, I can see why you're saying that based on the photo - it almost looks like there has been a chemical reaction but in actuality the paint I applied has not reacted at all and is just sitting on top of the other paint. I just checked and you can easily scratch off...
Ok guys please help, I need an expert!
Got some louvre doors from https://www.simplyshutters.co.uk/shop/interior-louvre-doors-white-line-painted-louvre-doors-p-89.html
They came: "painted in white to save you the laborious task of having to prepare and prime the wood yourself..." - To be quite...