I'm not a supporter of single manning. And I have a great degree of sympathy with the safety role of guards in (thankfully rare) contingency situations.
I do, however, think that - precisely because contingency situations ARE rare - and because of the rural nature of much of "Northern" - there is a huge degree of merit in the proposal that the driver should operate all aspects of the train in normal circumstances, leaving the second staff member to attend to customers, including ensuring revenue.
That said, I'd still have the second person fully safety trained (pretty much - a "guard"), and they would be required to instantly drop all other duties and responsibilities and adopt their traditional safety role, if and when a contingency situation arises.