Update: Commenting should be back to normal. Thanks to someone on the WordPress Support Forum who identified the culprit as an update that was applied this morning to the CloudFlare plugin. A new version of this plugin has corrected the problem.
There is a problem with email addresses being incorrectly flagged as invalid. It is under investigation. In the meantime I have suspended the check for a valid email address. Unfortunately this means that email addresses are not being sent and, as a result, avatars are not displayed and all comments are going into moderation. If you have an account, as all bloggers on here do, you will find it easier to sign on before leaving a comment – yes Kath, that includes you!