Building a wall at front of house

Hi
Just have a quick question. There is a hedge between myself and our neighbours that is gone really withered looking from the bad weather in early 2010. We thought that it might regrow but it hasnt and got even worse with the last bad weather. It is now nothing more than a lot of twigs. It looks really horrible..

Anyway, to make things complicated we dont speak to the neighbours - we do however want to take the hedge down and build a wall (we are willing to pay for this) I know that there is the requirement not to have it over 1.2 metres tall, but just wondering do we really need to ask their permission?

They would be the type that out of spite they would say no if we asked them. By the way the hedge that is there was paid for and planted by us many years ago (actually about a year before they moved into that house) My husband has always maintained it and they have never ever trimmed it at all even though it is split between both gardens.

Anyway, do we have to ask them or could we go ahead and build the wall between both gardens?

Any advice would be appreciated.

Your neighbours might object if you build any of the wall on their property, so you might find you have to build the wall totally on your side of the boundary if you don't want to consult them.

Thanks - I thought as much but just wanted to confirm..