Apologies to anyone who’s tried to reach this website in the past few days – I just noticed that it wasn’t loading unless I was logged in. A quick rummage through the logs revealed a problem with a plugin (W3 Total Cache) trying to grab more memory that permitted.
I don’t understand why I didn’t see this problem when I’m logged in, but I’ve disabled the plugin and everything seems to be OK again (both logged in and not).