Look at the pic I've attached. Its nothing new. Just a pic I found on some nissan site, prolly put together originally by nissan.
Max power 180kw@6400rpm
Weight 1380kg
Power to Weight ratio = 130.435kw per tonne
The law clearly states that a P plate driver shall not drive a vehicle that has a power to weight ratio greater the 125kw per tonne. Power is measured at the engine. Weight is calculated in the vehicles unladen stock standard form (that means COMPLETELY unmodified, no driver, no fluids, no cement or mates in the back).
The power and weight figures would have to come from Nissan if you wanted to contest it. You can weigh your car and put it on a dyno, but it aint gonna help.
You are breaking the law. End of story. You could waste a day in court trying to get out of it, or you can pay the fine. Stop whinging! This shit happens to everyone everyday!!!!