By 24 hour service, do you mean the same level of service all night and all day because in Tyne Rail's day that was certainly not the case. There were some services that ran late night/early morning around the Tyne loop but they were the exception not the rule. There were services that only ran anti-clockwise around the loop and bear in mind that there was a huge amount more industry on the Tyne than there is now.
I can't remember any services that ran to South Shields or Sunderland overnight but they also ran under the auspices of 'Tyne Rail'
You'll notice also that the night trains didn't stop at Manors. In my experience, when I rode these trains occasionally in the 1970s, there were ALWAYS some people who had managed to get access to Manors Station and it was qiute amusing to see their reactions (the speed of which depended on their degree of intoxication) when they realised it wasn't going to stop!
Forgot to add that the timetables I posted were from the Newcastle and Gateshead Bus/Train/ferry timetable from December1974 so those would be DMU operated.
I appreciate what you say about the nightlife in Newcastle I just don't think there is enough demand to justify an all night service. Perhaps a later service than now could be justified, maybe 02:00, but like you, I doubt many would like to work those. I certainly wouldn't want to be out and about in certain parts of T&W at that time of night, and I'm from there....
Back at a computer now so can get my words out a bit better. Looking at that timetable, you wouldn't really be able to call it 24 hours, and as has been said it would almost certainly have been to get workers to the shipyards or other industry which has long since disappeared.
Going back a few years now, BR decided to get rid of the Tyneside Electrics as patronage on the North Tyneside loop in particular was being hit by competition from bus but mainly the car. Introducing DMUs onto the services has been seen as a backwards step - electric trains have much better acceleration and braking compared to DMUs, so journey times increased and patronage again suffered. It also didn't help that the DMUs were not exactly in good condition. Added to this, BR were not really investing in stations.
Fast foward and the Metro was introduced. Decline of industry along the Tyne means trains running during the late night and early morning probably isn't needed, although there is the argument that trains could be running say once every half an hour to provide some sort of service. The main problems I see are:
The morning peak uses nearly all available stock that is not out for maintenance or at Doncaster. This potentially means a train that has been running around all night will need to be prepped for service or sent out without being cleaned etc
Vandalism would no doubt increase.
You would need more drivers to cover these shifts, and certain stations would have to be manned
There is currently only a 4 hour window for engineering, cleaning and other work to be done on the system overnight.
I thought it would probably be related to the tight maintenance regime for track and rolling stock these days. It was just that I was perusing the 1973 timetable and all night services on local rail routes were pretty rare (and still are). Also noticed they were 'Paytrains' at night too - couldn't have been a great deal of fun for the conductor/guard.