Yes, it is terribly slow today. Other non-blog bits on the same
website hosting are running fine.
The problem appears to be something to do with calling files using the include() function in PHP.
It is possibly something to do with permissions. I had a bit of an FTP finger-spazz yesterday and inadvertently set public_html to 777 for about a minute, then reset it to zero (which broke everything), then set it at 755 to "fix it".
Admittedly I have no idea what effects such tinkering will have but this weirdness started shortly after that, so it may be related.