We are often asked for hedging to block out a neighbouring eyesore. Also what is the current law concerning tall hedges, we can point towards some information. But the simple answer is, we don't know or that different councils have different attitudes to hedges and how high they should be, so it is probably best to ask your local council.
Usually there is not problem with hedges up to 6’6” (2m) tall. But the Anti-Social Behaviour Act 2003 relating to tall hedges, allows councils to take action where "reasonable enjoyment of a property is being adversely affected by the height of a high hedge situated on land owned or occupied by another person".
In 2004-05 the Government put together a very dry and mind numbingly tedious booklet (as pdf format) and calculation sheet (as Microsoft Excel (xls) format), so if your concern either way about yours or your neighbours hedging, knock yourself out and download them here.