My hosting service had some problems and did some emergency maintenance on both the database servers and the servers on which the site is managed, which took sites offline. For some reason even after they brought everything back online, the board was returning an error message and has remained offline.
It turned out that for some reason, their work changed the access permissions to the site. Their support didn't spot this but my partner and I identified the issue once we had the time to look at it (useful to have a programmer around!). A quick change to permissions and the site was back up.
Apologies for the delay but I was travelling to the US all day Monday and have had a mix of work and family events on through today and I didn't even notice the site was offline until late Tuesday California time. Because the hosting service had posted about ongoing issues to their support blog, I assumed things would be back online once they sorted this at their end -- only today did I realise the problem was persisting.