TechHead,
When people here talk about Diesel Helicopters they are talking about reciprocating engines (i.e. piston engines) powered by Jet-A1. Jet A1 has a freezing point of -47 Deg C and doesn't wax up like road diesel so is a non-issue.
Gaseous,
That is a scary thought for this industry... one stroke of the pen to double fuel costs... You can picture the scenario... JetA1 for "export" (i.e. international airlines) will remain the same, but any fuel used purely for within the UK (i.e. 99% of our domestic helicopter industry) will be taxed at the same rate as Avgas.... arrrrgggg