Hmmmm.
That's very odd. First of all, we've made no changes that would impact the performance. Also, it's weird that you would get taken back to a login page when you don't need to log in to read, only to post.
Have you tried closing and restarting Safari since you had that issue?
Also, I'm wondering if clearing the cache on Safari will help. If you don't know how to do it, here's how to get there: Open up the Settings app and find Safari in the left-hand list, and then scroll down the right side until you find the “Clear History and Website Data” button.
Let me know if either of those suggestions work for you.
I've tried closing and restarting Safari, switching the phone off and on again and I've cleared the cache, but nothing helped.
Yesterday it was playing up all day but it was working for a short while in the evening, and then today it was back to square one.
I tried going onto Digital Spy to see if the problem was with forums in general, but that is working fine.