Here's the idea: For the rest of this year, DON'T purchase ANY petrol from BP. NZ's biggest price up driver company.
If they are not selling any petrol, they will be inclined to reduce their prices. If they reduce their prices, the other companies will have to follow suit.
BP is a global company, there are many, many, many times the population of NZ who would be happy to buy BP's product at BP's price if every person in NZ suddenly decided to Boycott BP.
Like dairy products, fuel is traded on the global market, supply and demand, simple as that, demand (legitimate or not) is always going to exceed supply.
If you can't afford the petrol, don't buy it, but trying to force a fuel price reductions by not buying is like excreting waste fluids into a rapid moving air mass.