Thank's JimHDK for your reply.
Firstly this problem has only occured since i recently upgraded my phone from an Iphone 3.
To be perfectly honest it has only happened when trying to load video pages on an explicit website.Namely Pornhub.
I have tried restoring the phone although did not set it up as a new device, only restored to backup so as not to lose contacts etc.
I did not have this problem with the old handset.