If I had cornflakes for breakfast (which I don’t), I would have choked on them, reading Andrew Parker’s view of the threat posed by Russia, not just to the world at large – that is a commonplace of the “new cold war” discourse – but to the stability of the UK. With the majority vote for Brexit against the strong preference of Scotland and Northern Ireland for remain, we have shown ourselves quite capable of inflicting potentially fatal harm to our national stability all by ourselves. Why would we need Russia to do it for us?

That was a knee-jerk reaction to the main thrust of the MI5 chief’s first national newspaper interview in the agency’s history. But a second, more substantial, response chased behind it in the form of a rather basic, and recurrent, question. Why is the UK establishment in general, and UK intelligence in particular, so fixated on a supposed threat from Russia?

The cold war is a quarter-century behind us. The Warsaw Pact was dissolved; the Soviet Union collapsed. Today’s Russia has three quarters of the territory but only half the population of the old Soviet Union. Its GDP, whether overall or per capita, is far below that of the US, or ours. Its 2015 military budget took 5% of that – $70bn in actual money – less than an eighth of the nearly $600bn spent by the US. “Tsar” Vladimir Putin may have played a weak hand magnificently, as judged by admirers and detractors alike, but a weak hand is still a weak hand.

If Russia really harbours ambitions to reconstitute an empire, its only success to date is the expensive (in every respect) reacquisition of Crimea, a contested no-man’s land of ragtag rebels in the rust belt of eastern Ukraine, and two miniature enclaves inside independent Georgia. That recent “show of force”, when the might of the Russian navy made its stately progress through the English Channel, demonstrated only the obsolescence of the erstwhile superpower’s fleet.

In the same interview, Parker disclosed that there were around 3,000 “violent Islamic extremists in the UK, mostly British”, and that cyber, not just in Russia’s hands, was the threat of the future. So let me repeat the question: why does Russia remain bogeyman-in-chief?

Here are a few ideas. The first is that blaming Russia carries little cost. Russia is not China. Investment is not a big consideration. For all sorts of reasons, political relations have long been dire. Applying the same virulent rhetoric to terrorism conducted in the name of Islam, on the other hand, risks fomenting social and cultural strife here at home.

A second reason, now as in the past, is that blaming Russia aligns us comfortably with the US, where stalwarts in Congress and at the Pentagon have never emerged from their old thinking about the threat. The Russia card has been played to exhaustion during this presidential campaign, to the point where it could swing the election – and I don’t mean in Donald Trump’s favour.

A third factor is the consensus about a strong and malevolent Russia that still rules the “expert” community, and will probably do so for a few years yet – helped along by the hatchet-faced Putin. There are younger specialists who take a rather different view, but they are drowned out by the ingrained cliches. Note how quickly Boris Johnson was “turned” from the realist of his journalist days to the fierce cold warrior foreign secretary. Such a U-turn makes him look intellectually foolish – but no more foolish, some might argue, than he has made himself look on so many other scores.

Then again, all this anti-Russianism from MI5 could just be a front. Although it is hard to understand what purpose would be served by presenting Russians as scarier than jihadis or the gangsters who supposedly roam London in search of machine guns, disinformation is the stock in trade of intelligence services everywhere. Or – perish the thought – the judgments could just be wrong. There have, after all, been egregious mistakes, even where the material has been gathered and interpreted in good faith. Look no further than the data on Iraq’s chemical weapons, as assessed by Parker’s colleagues and institutional rivals across the Thames.

I wonder, though, whether the real secret behind the MI5 chief’s Russia focus is that it is starting to become harder to demonise Russia now. Time was when James Bond and the pantomime idea of a Russia threat were an easy sell – able to bolster departmental claims to a bigger budget. But look at the “below the line” comments on what Parker had to say and there is a current of dissent that cannot come exclusively from so-called Kremlin “trolls”. You hear something similar in phone-ins on Russian topics, where the voice of a sceptical public comes across loud and strong. For all MI5’s warnings, maybe Russia’s time as the UK’s all-purpose fall guy is nearing its end.