Clean it with 3m pad, prime n paint touchup.normal preventative maintainence.
I am taking that view. However, it would be very difficult to do proper prep work without stripping off lots of bits of the bike. The supposed beauty of hammerite is that little prep is needed, and I sort of have the feeling that the resulting coating may be more flexible and chip resistant than primer and ordinary paint. If I was a more careful painter it could have looked much neater, but it's tucked out of the way so it will do.