The first thing is to discuss your concerns with your neighbour. If he is
not responsive to your objections then write a letter to the council setting
out your concerns about the planning aspects. remember that even if he does
get planning permission then that does not mean that he has carte blanche to
build since he has to obey the law regarding trespass and the Party Wall
Act. He cannot force you to give permission to allow access for building in
any way. The Party Wall Act is available here
http://www.hmso.gov.uk/acts/acts1996/1996040.htm and note the sections
regarding adjacent excavation and construction.