Thank you all for your input.
This is the message I got form Ed on the new site:-
'Hi Tilly, that means we're not behind "HTTPS" - we use old fashioned "HTTP".
HTTPS used to just be used for websites where you sent senstitive data - like your card details. These days the trend is everyone has
HTTPS.
Because all your posts are public, it doesn't matter whether you send them to us encrypted. We have our own security measures in place, and
HTTPS wouldn't change any of those particularly, but it might seem reassuring to some.
AB is perfectly safe as it is, but we're likely to upgrade (i.e. pay for) an
HTTPS certificate in the near future because the perception that you've drawn attention to :)'
So it's safe to use. That's reassuring.