if its a 30 40B, GC 41 315 81, and its a Robert Shaw valve, you can get one from:-
http://www.mjtcontrols.co.uk/Part_Type3.aspx?Manufacture_ID=32&Part_Type=Gas+Valve
although it'll cost nearly £300, then find a fitter at a reasonable price, corgi registered of course.
freeze nomore, January 2010