On 19 Nov, 09:12, (Steve Firth) wrote:

If, as you say, the white paint peels off easily, peel it all off to
reveal the green painted layer. Having done this, or as much of it as
possible you need to sand the entire door to provide a key and to level
off any remaining bits of white paint. This is going to make dust, a lot
of it, and no matter how you arrange things dust will get everywhere.
Sanding by hand using a sanding block is probably best, because a power
tool will destroy detail on mouldings and is too aggressive for the job.
I'd suggest going over the entire door with 60 grit abrasive paper.
Somethign good quality such as aluminium oxide paper. Then go over it
again with 80 grit and then again with 120.

And wear a face mask.

Cheers
Richard