Military I think is 5 GCSE A*-C (English+Maths) and 2 A-Levels. After you've served in the military for a certain number of years you can then leave and join a civilian helicopter company that provides helicopters to the police. You could always go down the civilian route in which case you'd need to have A-Level standard qualifications to become a commercial helicopter pilot (don't know why) so I'd imagine good all round GCSE's and A-Levels. If you're focused on just flying for the police, you need to gain helicopter experience which can be done in the military or civilian e.g. Flying to offshore oilrigs, once you've built up your hours and have the necessary flying experience for example a certain amount of hours low-level, poor weather, night flying, then you can apply. I'd advise to go military as they pay for all your training but you could always get sent to fight abroad, nothing wrong with that, but thats a possibility. Police Officers don't need qualifications but have to be confident in communication. Some forces offer police officers the chance to become observers in their air support units. I doubt they train police officers to become pilots.
You need to first join the AAC,RAF or fleet air arm you will not be able to join the police as a pilot from school
You will need some science's and maths mainly good luck
This is my understanding of it all. To be in the Police you don't need any qualifications, just have good communication and written skills. The police heli pilots as far as I'm aware aren't in the police, they work for heli companies that give their helis to the police. Do become a heli pilot you need a ppl on helis then a cpl. This is expensive but a lot cheaper abroad ( about half the price than in the UK ). You could always join the military, learn to fly helis, then go civilian. If you want the best of both worlds, which is something I'm looking into, join the military police. Their pay is so much better than civilian police force. If you went into the military police with the army, their may be the chance to have a tour with the Army Air Corps and fly helis for a few years. The military police do similar stuff to civilian police, just get paid a bit more which if flying is something you want, its a good way to get the money for it.