ANDREW & HILARY MEREDITH
Just to add a few points to Richard's helpful advice, if the radiator goes down to bare metal in places when you sand it you need to use metal primer. You can get this in small tins. If any bits are rusty then you need to deal with that. Red oxide primer will do it and will also prime any bits just bare but not rusty. When you use undercoat make sure it is solvent-based (the old-fashioned sort) and not water-based 'quick-drying' stuff because that usually says ok for wood but not metal. And between sanding and painting (if this isn't too obvious to mention), get rid of the surface dust. I usually vac and sponge (in which case leave to dry) or use a cloth with white spirit. that can then be painted onto with solvent-based paint straight away.
