As I understand it, I may be wrong, avaition gets taxed less on fuel than any other vehicular use. This is the only way avaiation can exist at the levels it does.
Fuel as a percentage of total cost of operation of a helicopter is not insignificant, but it's not as big as many other of the fixed and variable overheads. Most/all of those overheads attract taxation of a sort, as well, so the benefit to the Exchequer is pretty high.