Without drawing any conclusions at all, the percentages of the vote (and distance from Tories) over the past 40+ years are interesting:
Blair (1997) 43.2% (+12.5)
Blair (2001) 40.7% (+9.0)
Corbyn (2017) 40.0% (-2.4)
Callaghan (1979) 36.9% (-7.0)
Blair (2005) 35.2% (+2.8)
Kinnock (1992) 34.4%...