I'm in the middle of reading The Natural Building Companion and have to say that it is really good. My attitude started a bit cool - it was a book I thought I had to read. And it's taken me a long while to get through the first chapters. But then I got to the chapter on foundations and found lots of useful information. And then the airtightness details! Far more explicit than anything else I've seen. The DVD is also helpful, depending on how you view video in books.

http://www.chelseagreen.com/bookstore/item/the_natural_building_companion:paperback%20+%20dvd

One of its strengths is that it is explicitly about building houses in the north-east of the United States. So they are open about their biases, and most of the biases are also applicable to the UK. You do have to allow for strange product names like Masonite (hardboard) and Homasote (not quite sure whether there is an equivalent?) and especially be aware that most of their examples use a timber frame. I confess that I'm viewing it with my own bias, and I am a balehead; a loadbearing balehead. You also need to watch out that you're not ripped off for the price!

I'm still reading, so I don't know how the story turns out.