It seems that disruption to the site comes in waves, and we're down again at the moment. The site went down just after midnight as I was going to bed, so I switched off thinking it was a transient glitch. This morning I couldn't access the site, and the d'base server was timing out too, so I'm guessing there's a hitch at the hosts' end. I've contacted them in case they don't know yet, and now we sit tight... Normal service will be resumed as soon as possible.
EDIT: 12:30pm and we're back. Looks like a DDOS attack overnight, which our IT bods have been working hard to sort overnight. They're bleary eyed this morning, and I'm sure you'll all join me in saying "thanks" :o)