No, the problem was ocurring both when I was in range and out of range of my home wifi.
After posting my original message i continued playing around with the phone and managed to 'solve' the problem by switching everything off, and then back on again. There were a few worrying moments after switching on when all my photos seemed to have disappeared!! but everything just seemed to sort itself out after a few minutes.
I still don't really understand what the problem was, or how it got solved
but at least it seems to be working again now.
Thank you for taking time to reply.