Double row crankshaft gear, of good quality and made in the UK.  This is the standard replacement item for Triumph TR6s, it may also be used as a durability upgrade for single row chain systems found on Spitfires with the late 1300 engine and all 1500s, GT6s and TR250s (you will need to replace the rest of your single row timing components with double row components to complete the upgrade).
July 2011: In the past year inexpensive hardened cam and crank gears have come onto the market.  These gears are made in India, and while they are indeed hardened, the quality of the gear teeth is sub-standard.  Additional, for crank gears, the keyway is machined inaccurately.  The result is a sloppy, yet hard, component that will give imprecise timing in addition to increased timing chain wear.