I rebooted my phone, which had no effect. Then I sent myself a test message to see if it would come through. Not only did it arrive, but it also somehow cleared the blockage and all my outstanding messages came through over the next few minutes. Including this one that Vic sent to me when I was at work on Tuesday:
You should buy a new toothbrush ... found it on the floor with the handwash, dettol, and loo roll. Not quite sure what Daisy was up to but I wouldn't risk it.
Two days ago.