One of the hard disks on the machine that runs this blog has failed. Accordingly, I'm scheduling a drive replacement, hopefully around 9am tomorrow. The blog and website will be offline for up to a couple of hours when that happens. I'll update this note when we're online again.
In order to reduce the risk of data loss I'm going to disable comments on the blog when I go to bed tonight (probably before midnight BST, 8pm EST).
Update
Hard drive replaced and everything working again as of 10:30am.