Are you coming to the site from a bookmark? If so can you delete it, and come to the site through your browser and then re-save the bookmark? HTTPS was recently added to the site so if you're using an old bookmark that was added without HTTPS then that's what could be causing the issues.
I access the site from an icon saved on my iPad or the 'top sites' feature on my macbook. I've now saved a new icon on my iPad and deleted the previous one, and I hope that does the trick. I suspect that last problem I had was when I first used the iPad after thinking I'd sorted it on my macbook. I'll see how it goes. Thanks Niall