Aha! I was wondering when somebody was going to ask me about that. I use some metal cleaner called autosol it costs about £5 from halfords. When i picked my car up the exhaust was black!

Abit of elbow grease later and hey presto chrome. Mind you i did use some wire wool and lightly remove the rust build up on it took me about 25 mins to get it looking like this.
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Colorado Red 07 Plate ST
Mountune CAIS - 60mm Throttle Body - Full Resonated Milltek System - Bilstein B12's - 300mm front discs - Gloss Black Team Dynamics Pro Race 3's - Tints - Red-Black DMB Badges and loads of eBay stuff...