Hi Seamoor
The Farnes is awesome !!
You could visit my local patch at Low Newton/Beadnell Bay a few miles south of Seahouses (where you get the boat), there's a great arctic & little tern site at the Long Nanny Burn... well worth visiting, the tern wardens hut is right in the middle of the action so you get good views. A few bits there today... little gull, bonxie, arctic skua and a few manxies.
There are quite a few caravan sites up here, not sure if they take tents, but there is a camp site about 2-3 miles south of Seahouses at Beadnell. Its just on the northern edge of Beadnell and the main coast road goes right past it.
Is there anything you particularly want to see ?
Northumberland coast in general has loadsa great birding, there are loadsa well known sites from Holy Island south..... Budle Bay, Farnes, Newton, Amble/Coquet Island (for roseates), Hauxley, East Chevington, Druridge, Cresswell.... etc etc...
Feel free to drop me an e-mail if you need anymore help....
G