Sorry Jeremyd
But you cannot get a free copy!
I've just ordered 15 copies for my students and tried to find a free source
Typical cost is about £45 and dont forget the IEE On-site guide at about £14 because not all the info is in BS7671
You can get a version on CD-ROM
You may get some useful info from the NICEIC site
Try some of the electrical wholesalers sites for freebees