Hi Uncle_Bob_2,
My last visit to the Apple Store has resulted in an escalation to Apple to see if the update in May/June has somehow created this problem (the phone was definitely OK prior to then, as I did house viewing videos on almost a daily basis and never experienced this problem previously).
I manged to capture the issue, by videoing the phone videoing from another phone and have sent this footage through to Apple (I must admit explaining the issue resulted in some puzzled looks, so it was nice to have the evidence !).
My reflection is that it isn't the camera (I've had a new one fitted), it isn't the phone (I had a replacement handset and it did the same) and it isn't anything previously stored on the phone and restored (I performed two complete manual deletions and had to restore everything manually, to save restoring what might have been a bug from previously stored files, etc.).
I'd stated in a previous post that I felt that this was a bigger problem because ordinarily people don't shoot video longer than 2 mins and I still stand by this.
So in summary, my view is that one of the updates has caused this and (fingers crossed) one of the future updates will fix this.
The gentleman that I last saw at the apple store has been excellent in both his advice and also keeping me updating on progress to date.
Regards,