The tall, lean look, the narrow face with high cheekbones, the aristocratic charm, the walk, the intonation, the angle of the head, the ponderous, rigorous manner in which he sets out his thoughts - all these familiar characteristics would have been enough to make poor old Harold Wilson wake up screaming in the night, were he still alive.
But this is not Tony; it is a new Benn. Hilary, the new Secretary of State for International Development, is the third scion of the Benn dynasty to join a Labour cabinet (and probably not the last, given how many politically clued-up Benn children there are at various schools around London). He reached the top rapidly, only four years and four months after he first entered parliament. For comparative purposes, that is just a few months longer than it took Gordon Brown, Patricia Hewitt or Charles Clarke to travel the equivalent distance, but faster than Tony Blair. Unlike any of them, he managed the feat of getting all the way up without making serious enemies.
If the physical resemblance between father (Tony Benn) and son is remarkable, so is the contrast between the family loyalties that tie them and the political gulf which separates them.
Benn Sr was never famous for tolerating people whose political opinions were different from his. Anyone else with a career path like his son's could expect to be the target of some caustic entry in the Benn Diaries, writing him off as a "Blairite hack" or something worse; but for Hilary, whose name appears dozens of times, there is a constant catalogue of unashamed paternal pride, mixed with outbursts of anxiety when his boy is ill or unhappy.
When Hilary finally secured a safe seat, having been adopted for Leeds Central after the sudden death of the sitting MP, his father gave him advice and moral support. Sometimes the advice was a little too esoteric to be of much use on the doorstep, as when he drew his son's attention to a reference to the class struggle in Leeds in the early 19th century, to be found on page nine hundred and something of E P Thompson's Making of the English Working Class. Nevertheless, it was the thought that counted.
And when the younger Benn formally took his seat, after a by-election distinguished only by its record low turnout, his father stood alongside him as his sponsor. Several of those who witnessed the ceremony say the old man was so proud, he was crying.
Yet it would be obvious nonsense to say that the younger Benn's ascent is the result of patronage. It would be truer to say that, for someone of his natural ability and political acumen, he would have risen much faster if his name was not Benn. On the other hand, if he had not been a Benn, could he have accumulated so much political knowledge so early in life? At nearly 50, Hilary Benn may be one of the youngest cabinet ministers, but he is probably the only member of the government to have met Clement Attlee.
There is a piece of television footage which may or may not have been preserved in a vault of the CBS television network, of a nine-year-old London schoolboy telling American viewers in summer 1963 that "the hereditary system is ridiculous and Britain ought to have a president who is elected, instead of a queen who is not".
By that age, Hilary Benn certainly knew about the hereditary principle: he had been accompanying his father on daily visits to the high court, where the judges eventually made constitutional history by allowing Anthony Wedgwood Benn to renounce his inherited peerage in order to hold on to his seat in parliament. Although the judges looked weird in their wigs, the little boy understood that his father was fighting for his job. While he was temporarily excluded from the Commons, he was having to disappear to the US on lecture tours in order to make ends meet.
Another piece of old footage which may pop up one day to embarrass the new International Development Secretary is from the Labour conference of 1978, when the party was debating whether the UK should leave what was then known as the Common Market. Hilary, who had campaigned alongside his father for a "no" vote in the 1975 referendum, rose from the floor to deliver what his doting father described as a "super" speech - a comment backed up by the correspondent of the Yorkshire Post, who apparently did not recognise the younger Benn and simply recorded that "the conference was electrified by a young delegate from Acton".
Hilary Benn's best-known comment is that he is "a Benn, but not a Bennite", which is generally interpreted as a gentle renunciation of his father's left-wing radicalism, though Tony Benn himself always abjured the term "Bennite", even when his influence was at its height. He made the claim 20 years ago, when he stood as a parliamentary candidate in Ealing North, though at the time there was good evidence that he was both. But that election appears to have come as a salutary shock. Ealing North was one of many constituencies that went from being a marginal to a safe Tory seat (and has since swung back to being solidly Labour). The 1983 election was Labour's worst postwar defeat, and was fought on a long, prescriptive manifesto whose principal author was Benn Sr. Hilary himself has admitted having an uncomfortable time defending that manifesto to the Ealing voters. Some time after, he became in every sense "a Benn but not a Bennite". The father moved sharply left while the son shifted equally decisively in the opposite direction.
As head of the policy and communications department of MSF, the white-collar trade union, he was present at one of those pivotal moments in Labour history, when John Smith was trying to persuade the unions to agree to end the use of the block vote in leadership elections and in selecting party candidates. This vote, at the 1993 party conference, cleared the way for Tony Blair and, in a close contest, it was the MSF's last-minute decision to back Smith which finally clinched it. Benn was at the vital delegates' meeting that opted to support the leader.
His personal philosophy now is that politics is about achieving small, mundane things to improve the lives of others. Whereas his father thought in terms of sweeping whole establishments away and turning the political order upside down, the son worries about the small print of reformist legislation. This helps explain the very positive reaction to his appointment from charities operating in the third world, overseas aid being a matter of dealing in detail, rather than in the construction of billion-pound dams.
His career as a minister has so far been short of controversy. The one time he ran into public difficulties was as David Blunkett's deputy at the Home Office, earlier this year, piloting the Sexual Offences Bill through the Commons. This worthy piece of legislation aimed to put a final end to discrimination against homosexuals by making all laws on public decency apply equally to gays or heterosexuals. Although it legalised anything that gays might do in private, the bill also struggled to retain the law forbidding "cottaging", for the benefit of men who wanted to be able to use public lavatories without being unwilling witnesses to man-on-man action.
As he presented this legislation to MPs, Hilary Benn had to admit that the clauses on sex in a public place were drafted in such a way as to make criminals out of married couples who nipped out for a spot of nookie in the garden - but at the same time it allowed casual liaisons in a public toilet "provided the cubicle door was closed". The bill is still struggling to get through parliament. And yet, the memorable point of the story is not that the minister was caught spouting nonsense - because anyone setting out to draft legislation against sex in public lavatories while ensuring it applies equally to heterosexuals and gays is likely to arrive at a nonsensical conclusion - but that no one, not even the most anti-Labour newspapers, concluded that Hilary Benn was either malevolent or stupid.
It was as if the younger Benn had pulled off a trick that had eluded his father. Tony Benn continually exhorted politicians and press to concentrate on "ishoos" not "pershonalities", only to have his own personality subjected to relentlessly hostile scrutiny. The much-reviled British politician of the 1970s and 1980s has a son who is one of the least reviled cabinet ministers of recent times.
Andy McSmith is political editor of the Independent on Sunday