Bill English has a degree in English, which should have inculcated respect for correct word use — if he hadn’t become a politician, a breed which bends language for good and ill.
So in claiming not to break an election promise not to raise taxes, he asserted his new airport levy is not a tax. The Shorter Oxford Dictionary defines a levy as “a tax, esp. one raised for a particular purpose”. It is a hypothecated tax, as the petrol tax is.