What exemption would be needed?
I am pretty sure that an exemption isn't required.
All the Unit management have to do is produce a written explanation and a safety case for extending the 40nm limit and SRG will consider it accordingly.
This sort of thing usually is associated with providing a LARS service, something Newquay are a long way away from being able to do.
Even if they didn't want LARS, providing a radar service beyond 40nm in a Class G airspace environment, has a significant impact upon single radar atco workload, as I suspect Newquay management have only budgeted for.
When it comes to ATC manning, it would appear that the management are trying to do it on a shoestring budget and that those daft enough to accept the terms and conditions offered will soon get fed up of working maximum hours for minimum time off and relatively crap pay.