The new element in the follow-up is an intervention from former MI6 chief, Sir Richard Dearlove, arguing that Corbyn was the subject of a 'classic cultivation.'
Such allegations are all too easy to make. Intelligence is about people and information, but so are politics, diplomacy and journalism. What sets intelligence apart from other forms of professional networking, if anything, is its clandestine nature, but there is no evidence that Corbyn betrayed any secrets. Rather, the evidence is consistent with his characteristic openness to all comers.
The Sun underlines the dirty tricks heritage of this kind of story, by alluding to the case of the former Labour MP John Stonehouse, alleged to be a spy by Czech defector Josef Frolik in the late 1960s.
That claim was questioned some years ago by Stephen Dorril and Robin Ramsay in their biography of Harold Wilson, Smear!
Their chapter, The Czech Connection, shows that MI5 knew about Czech approaches to Stonehouse before Frolik defected. They suggest that MI5 took no action because Stonehouse had reported the approaches himself, as he claimed, and as other Labour ministers were known to have done. The Frolik story was nevertheless kept alive, in their view, because it provided a useful smear against Harold Wilson in the run-up to the 1970 general election.
The long tradition of intelligence attacks on the Labour Party famously goes back to the Zinoviev Letter of the 1920s. Some will be tempted to see Dearlove's previous attack on Corbyn, on the morning of the 2017 election, in the same light. Surely, an intervention prompted by serious concern for the public interest would have been better timed earlier in the campaign, when it could have prompted serious scrutiny, rather than at the last minute?
On the other hand, it could be said that Dearlove's role in bringing about the Iraq War, which helped to discredit a generation of British politicians, did much to pave the way for Corbyn itself.