If you're doing the work yourself then you should be looking at self build insurance - get a few quotes - try the products and services links above
I used these people but never needed to claim so can't comment on that aspect http://www.selfbuildzone.com/
If you're using a main contractor then check what cover they have and if you are mortgaged the buildings insurance they will require before you begin.
I took out accident & life for myself with the above as I was labouring on my own house, I also got covered for employers liability as I directly employed some labour and didn't want to be bankrupted by a site accident YMMV.
