I got this RESOLVED following your advice!
Indeed, I only forwarded HTTP Port 80, whereas the manual requires that three other ports be forwarded as well, namely:
Command Port: 6001
Media Port: 6002
Mobile Port: 6003
I didn't realise I must forward all four ports - I thought that forwarding just port 80 would be sufficient as I would only be using IE web browser.
Thanks for your great help, alpine0000 and ssmith10pn - without you I would still be in the woods! I followed you advice exactly, went through the manual, found three other port settings and bingo! Can view the cameras from outside my LAN!