Looks like everything is back for now.
No explanations have been forthcoming and this is the second time within two months that it has happened, which does not leave me full of confidence in them.
I have been tweaking the blog a bit as there is an option to add extra "pages" to make it more website like - so that it can be more of a standalone thingy (technical term here, you understand) in the absence of the complete site. The module that puts the links to the pages on the blog doesn't seem very customisable, and the were too dark to show up on the dark background, so I have changed to a lighter one.
This time I really will look harder about getting the whole lot properly hosted independent of my ISP and also find myself a cheaper ISP that doesn't give me this grief.