Thanks for all your comments, but I do not have any SEO plugins installed on this. Also, I do not have any links to zapto.org, according to Google.
As I say, it might just be a coincidence, but the only thing I did to the site on Friday was to upgrade the Graphene theme, which, by the way, is a third party. I installed no plugins last Friday, so I think I can pretty much rule those out.
