Drink driving

• Can I be arrested if I am sat in my car drunk (over the permitted limit), but not driving?
• Can I be charged with drink driving if I am over the limit but just sat in my car?
• Do the police need a reason to stop me whilst I am driving?
• How much alcohol can I drink and not be over the limit?
• I know someone, who drinks and drives all the time, what should I do?
• If I suck a copper coin, will it invalidate the breathalyser test?