If you can remember the 1960s, many are said to have said, you weren’t really there. But if Britain fails to remember the 1970s, it may soon find itself in a place where it really should not want to be. Towards the end of the latter, infinitely less entertaining decade, a good number of those at the top of Jeremy Corbyn’s opposition Labour party made their political debut as members of a hard Left that was far less of a fringe than it deserved to be. They have come a long way since, but their thinking has not, and with …