Thank you very much for all your replies. I'm beginning to think I didn't have a problem but the fault lay with my internet conection.
I did have the Nectar toolbar but I'd had it for well over a year without any problems, but I tried uninstalling the toolbar last night anyway to see if it made a difference. The Freecause page didn't appear again but still pages were taking forever to download. I tried system restore, clearing cookies etc, altering browser settings - everything recommended but it was still playing up, sometimes pages loading as normal and other times taking forever, odd occasions displaying "cannot connect to the internet". I was convinced it was a virus or spyware until I spoke to my dad this morning who is with the same ISP (BT) - he has been having the same problems and only over the last two days like me. I did check BT's system status and there were problems in our area yesterday and the day before, but they were apparently resolved by late afternoon, so I assumed it wasn't that. This morning everything seems to be back to normal with pages loading straight away, so I can only assume it was BT's end causing the problems.

Thanks again!