Thanks for all the replies.
It looks like it is/was a network issue, as the connection has been stable now for over a day.
Normally tho when I've seen network issues before, its been the Receive/Send/Online lights which cycle not the Power/Receive/Send/Online.
It does say on Robins site that spontaneous reboots can be caused by a low signal level tho, so perhaps thats what it is??
Anyway glad to be back online, although still no contact from NTL! I'll see how the connection holds up and ring back if it goes down again.