Silver roof bars

Carplan do 2 products which I find very good both in a can with integrated brush

Interior valet and stain valet I think they are called, they are about the only thing I buy from asda!

I use the interior valet to freshen up fabrics and the stain valet to clean if they are dirty

Regarding roof bars are they scratched? Otherwise brasso metal polish should bring them up a treat

They're usually lacquered metal so you shouldn't need a metal polish unless they're very bad.

I'd use Werkstat Acrylic Prime: Werkstat Prime Acrylic | Werkstat Car Care & Detailing Products

This will clean them but also lays down some sealant so should help prevent tarnish in the future. If they get to a very bad state thn they get beyond repair and have to be replaced so protection is a good idea.

You can use Acrylic Prime on paintwork, wheels, glass and metal parts such as exhaust tips too - it's very versatile.

Strangely I used Werkstat Satin Prot (i know its a product for interior use but it did the job) and it brought my bars up excellently, no more milky looking markings. Whacked some sealant on afterwards for protection.