just spoke to the guys at mbppowersports.com, and have brought an M2 (V.A.L.E) ally silencer plus noise insert for £329 all in. 
Have been after one of these since the BMF last May but couldn't find an UK importer. The M2 is slightly smaller in width (oval) 3.75inch (M5 4 inch) so the BMW panniers should fit ok. Hope this is of use to someone. It sounded and looked supperb 
by the by, I even interupted the blokes scran so i could here it. LURRRRRVLY
Have been after one of these since the BMF last May but couldn't find an UK importer. The M2 is slightly smaller in width (oval) 3.75inch (M5 4 inch) so the BMW panniers should fit ok. Hope this is of use to someone. It sounded and looked supperb by the by, I even interupted the blokes scran so i could here it. LURRRRRVLY
