Right, finally fixed. This post is just briefly what I did in case anyone eklse has this issue.
First, I tried removing the older kernels manually to free up some room on /boot:
but the same issue kept repeating on running:
385 rm /boot/initrd.img-3.2.0-29-generic-pae
386 sudo rm /boot/initrd.img-3.2.0-29-generic-pae
387 sudo apt-get remove --purge linux-image-3.2.0-29-generic-pae
so, I decided to have a look at what was actually in /boot, and then (a bit recklessly) used:
sudo apt-get -f install
to remove some really obsolete kernels. I only actually removed 126.96.36.199 and 188.8.131.52 by this method.
Emacs and updates would then install as I wanted. I'm going to do a bit more housekeeping now to free some more room on /boot so this doesn't happen again.
Thanks for your help