Just checking to see how you went with your council. We are also in a similar situation and the neighbour has sent us the shadow diagram below
http://s1296.photobucket.com/user/raj_paras/library/
I am trying to figure out what options we have, if any.
Unfortunately the council were absolutely useless. I wrote them a long letter on why it would affect us and asking go advice on what could be done. I got one sentence back saying they couldn't do anything.
Luckily for us the double pulled out as the block wasn't big enough for the house they wanted. So we are back to having no neighbour and the chance of it going either way.
I feel for you. I know how it felt for us and even if people don't understand or the neighbour doesn't mean any harm, they just want their dream home, it can still be devastating. It wouldn't hurt to write to your council. Ours may have just been particularly useless! If its any help, I could send you the letter that we wrote just in case it helps you write yours. If that would be helpful, just let me know your email address.
All the best with it. I really hope you get somewhere and if not I hope it doesn't affect your home too much once the double is built.