Bill gurgled happily, sounding much like they
were saying:

Hi all,
I have 40m square of steel sheeting to paint, mostly still covered with
its original paint but also with a fair amount of rust caused by scrapes
and scratches, Obviously the ideal answer would be to sand it down,
prime and paint but to be honest the finish does not need to be perfect
so I am looking for a quick fix. Is there anything that could be
painted on either as a primer or final coat that is not going to mind
going on top of rust? All thoughts gratefully received, thank you.

Whatever you use, you need to clean it up. The only question is how
thoroughly - and that depends on how badly you want to keep it.

I've just asked an online supplier a similar question regarding car
undercarriage. Their answer was to clean it back "manually" (ie wirebrush
etc sufficiently to clean all the flakiness and loose muck off, but don't
worry about getting it all spanglingly shiny) and use Rustoleum 769. A
chunk of change from £20/litre, mixed to whatever colour.