My fault, sorry.
I'd not paid the hosting invoice in time. Have now paid several months up front, so lights should stay on for a while!
The fact that it took about 16 hours to realise should show how busy I am, I also forgot to pay myself my wages yesterday.
In fairness, I did warn people about how busy I am at the moment, but shouldn't happen again. Only took literally 2 minutes from finding out to going live again, I should probably dish out my phone number to a few people for things like this, an SMS would have vibrated in my pocket.
Apologies!