Thanks for the tip.
But I will proceed with the migration to Simple:Press because it’s a nicer interface for readers, easier to use, and there are a bunch of people at the end of their website who look after it for a living – BBPress (which is what we’re using now) is too hard to fix, especially when someone comes up with a handy plugin then wanders off to do something else after a year or so and it goes out of date.
For instance, when I tried to split this conversation off to a separate topic, it refuses and comes up with “A variable mismatch has been detected” when I go to the BBPress help page, there are others with similar problems but no solution offered after 18 months!
Changing horses is definitely on my ever-lengthening to-do list