Blocked Rights of Access

[Lucydashy]

I live in a middle terrace cottage (200yrs old). The end house has recently somehow been given planning permission to build a house attached to the end of our row. The problem is, this new house is directly on our right of access as detailed in all our deeds. Although the deeds do not give dimensions they can be worked out through the diagrams. He's started to build and has blocked our access without our consent. He has offered a route round all the work but the point is that it is our access, the route he has allowed isn't wide enough and the houses have utilised the access for the 200 years that they've been there! What Can I do to stop him building?