Yeah, T.P. O'Connor. Who held said constituency - and always as an Irish Nationalist - until he died in 1929.
As for Durham City, the incumbent for the old City constituency actually held on by about two hundred votes in 1918, but was easily beaten in 1922 and that was the end of that. Btw, if you ever stumble across it, Beynon and Austrin's Masters and Servants: Class and Patronage in the Making of a Labour Organisation is excellent on that general period in County Durham's political history.
Thanks, I will look out for it.