dust - Oh gosh, that would drive me mad too! It can be a bit of a curse, when dealing with someone like that, to be as far-sighted and as good at planning ahead as you are! I hope the issue gets resolved quickly.
caspiana - oh my goodness, that is a deadline and a half for the work! I think there might be some things you can do here - others can probably advise better than me because we never really had a firm end date - but I do know some people build in clauses where there is a penalty if the build runs beyond a certain date. You might want to budget for a post-build clean as well - I understand some companies do this in a two-wave process, with a 'dust clean' and a 'sparkle clean' after. Trust me, when you've seen the dust from the knock-through, you'll be glad you did! An orangery sounds absolutely lovely, by the way.
I am intrigued by "bear protected trees"!!! Where are you if that's not too nosy a question! 