I have changed the behaviour so it will detect if http:// is already there. Euan you might also like to know that you can edit your post by clicking the "Edit" link above it, so if you make a mistake you can correct it without having to add another reply.
Ah Trevor!
I have spent a lifetime sitting at the back of the class day-dreaming productively, but you are right: Mick's words deserve to be read closely. Never mind, Chris has come to the rescue once more.
Thanks Chris,
and can you solve one more oddity? Discussions is now open to anyone, but new contributions don't show as blue, updated, there (yet). Quite logical in some ways, but for several days I wondered if everyone had gone on holiday until I logged in out of habit.