Unfortunately there are no restrictions on the height that hedges/bushes can be unless they are Leylandii.
If a hedge does adversely affect the owners/occupiers of an adjoining domestic property then they may be able to take action through the High Hedges complaints system introduced by the Anti-social Behaviour Act 2003. The complaints system specifies the type of hedge and the adverse effects that it covers and, if you have concerns about the effect a hedge is having on your property you should contact the your council to see whether the High Hedges complaints system is applicable to your circumstances.
If you would like further information, or would like to discuss a high hedge, you may contact the Tree and Landscape Team by email at email@example.com giving your name, address and your reasons for concern.
High Hedges Prevention (.pdf)
High Hedges Complaint form (.pdf)
I have been informed by Planning (1/5/2015) that unless the complaint form and fee are submitted CBC are unable to enter into any negotiations regarding high hedges, as the local planning Authority would be inundated with similar requested and do not have the resources to meet the demand.