Widdybank farm is the HQ of the scientists working on Moorhouse and Upper Teesdale nature reserve - its unlikely thet they'd let you camp there.
The other campsite at Langdon Beck seems to haev closed and recent enquiries at the pub were a bit negative as regards camping on their lawn (I think they'd should reconsider this!)
There are camping spots by Maize beck, though strictly speaking its not allowed. There's also a very good spot by the olf flood-route footbridge which is a mile or so upstream from the new footbridge on the main PW route.
But dont tell anybody about it!!!