First step - speak with your neighbour
If you are troubled by your neighbour's hedge, the best way to deal with the issue is to talk with your neighbour.
Calling in the council or going to court (especially without first approaching your neighbour), might make matters worse. It's in both your interests to try and sort things out between yourselves - after all, you have to continue to live near each other, so it's better if you are on good terms.