Further advise can be found on the Communites and Local Government wesbsite:  http://www.communities.gov.uk/publications/planningandbuilding/partywall

Wikipedia has a bit of background on Party Walls http://en.wikipedia.org/wiki/Party_wall

The London Borough of Richmond Upon Thames also outlines the procedures  http://www.richmond.gov.uk/party_wall_act_1996

A full copy of the Party Wall Act can be found at: http://www.legislation.gov.uk/ukpga/1996/40/contents