According to this (http://www.acma.gov.au/WEB/STANDARD/pc=PC_90054
) VHF Band III uses 174-230Mhz and L Band is around 1450-1500Mhz.
If the Sharkfin only does L Band and in the UK they need an additional antennae for Band III then I think we're out of like being able to retrofit this and have it work with the current Sharkfin
Looks like AutoDAB is our only choice! Really keen to see how you go luster with your install. Good luck!