How do you know that the police were going to stop you for drink-driving? They might have been going to tell you that your headlight was out.... and if the worse came to it, you could (hypothetically) still be over the limit in the morning They probably can still do you for parking without permission when asked to stop by an officer of the ler. Let us know how the hypothesis gets on!
Most motoring offences aren't 'arrestable'. Drink-driving is. The police are empowered to force entry into a property (including a car) in order to make an arrest or to prevent an arrestable offence taking place. (Simply being in charge of a motor vehicle whilst 'over the limit', even if you're parked legally, is still an arrestable offence). So, yes, after trying to wake you and to get you to open the doors, they probably would smash a window.