In reply to David Barratt:
I'll see if I can dig out some specifics, but there are insurance companies that will cover stuff in a tent. You need to look at more expensive and heavy duty policies though. I got good cover last year through an 'extend holiday insurance from abroad' service. It was basically an expensive policy available on request from a specialist broker, but it explicitly covered loss from a tent or pack.
My house contents insurance now covers the valuable stuff for camping or car thefts, as well as an allowance for loss of other possessions and currency when on the move. If you travel a lot it might even be worth upgrading your contents insurance to get this cover?