I have made my bracelet now but still appreciate you're answer as I will know now for next time.
In the end I tied in a double knot (shoelace knot) and put some superglue on it but by the time I had done that the knot was too big to be hidden inside a bead so I just left it showing which was a bit annoying but still looked pretty. I think you must need a bead with quite a big hole in to cover the knot.