I seem to have sorted out the problem with my website. Tiny things can throw everything else out of place. It all came down to the size of my logo at the top which should have been made to fit 505×95 pixels exactly. It had been fine up until now, but I upgraded something yesterday and that must have altered something else. Ah the joys of running a website.
Many thanks to Michael Thorn of the children’s book website,achuka.co.uk, for pointing out the problem. I don’t know there’s a problem until someone points it out!