Just had a metal frame polished by a local Company who I can recomend. They also recomend using windowlean Original Cream for the cleaning of metal before applying a wax polish as it is abrassion free. They use it for their show pieces. It certainly worked on my frame.
Medway Buffers and Chrome, 4 Dickinsons Court , Enterprise Close, Medway, ME2 4LY. 01634 717515.
Hope this is of interest.