I suspect you have painted (a water based paint) over an oil based paint. That's probably why it isn't drying. And it will never stick.

 

You need to sand back, undercoat it and then paint it in an aqua enamel paint which is more suitable for doors.

Thanks for your help. You are all right I have obviously used the wrong paint and will have to start again, this time thanks to your help I know what I should do. I did try to get out of it cheaply and use old paint I had in the shed. Just proves being a senior doesn't make you smart.