Image copyright Getty Images

These days it's not that weird seeing a man born in 1949 rocking the crowds at the Glastonbury Festival.

Bruce Springsteen, Tom Waits and Richard Hell were all born that year and I am sure they could still get the campers roaring. The novelty value was that it was a politician, Jeremy Corbyn, who was lapping up the love this year.

However, the age gap and the "well, fancy that" factor have obscured the very real importance of the Labour leader's appearance at the annual music festival.

His first big gig since his election triumph (no, I know he didn't win, and yes it was) highlights the reason he's done so well, and flags up the pitfalls ahead. It could mark the point of peak Corbyn.

But a big deal? Certainly.

It won't get the column inches or hours of airtime and earnest analysis devoted every year to the leaders' speeches at conference time, but it was far more important. They rarely amount to much - trust me I've covered quite a few of them in my time - and they're nearly always forgotten within the week.

Mr Corbyn's offering was, to say the least, unusual. And that is the point. He doesn't play the game - and people who can't bear political game-playing love this conscious vibe.

Of course, part of its importance was the venue.

He wasn't speaking to party press officers and political hacks in a cavernous hall, but live and direct to thousands of people in a muddy field in Somerset. That the rebellious and radical leader of the Labour Party, scorned by the establishment and most of his own MPs, was asked to make a speech, is part of the meaning.

Image copyright Getty Images Image caption The Glastonbury crowd differed greatly from a traditional party conference audience

The organisers knew he would be popular. It is obvious that Jezza has become, if not an idol, an object of affection for some younger people.

That isn't particularly strange. Strands coexist, neo-liberalism may still rule the world and Glastonbury is an intensely commercial gathering, but Che Guevara is still on people's T-shirts and Margaret Thatcher isn't. Conservatism has rarely been cool, even under Dave Cameron.

Corbynmania isn't just retro chic with a dash of post-modern irony. The counter-culture moulded the modern. And - just as Glasto isn't really only for or about the young - this is only the symbolic tip of the Corbyn iceberg.

Festivals are largely made up of the unbuttoned middle class, pretty well-heeled, but no less fed up about the future and the society they in which they live, particularly after the Brexit vote. The part of the old Labour coalition who drifted away after Tony Blair's Iraq war.

But the tone of Mr Corbyn's speech was also really important.

He didn't pull that trick of daring but arrogant bands and hit them with new material. He stuck to some of the very old favourites, but there was a freshness for those who've heard thousands of political speeches.

There were none of the policy announcements which are catnip to the commentariat and only a couple of disparaging comments about President Trump, but no direct attacks on the Conservatives.

There was not much mention of current politics at all in fact - one reference to the Grenfell Tower fire and one about rights of EU citizens and that was about it.

Instead, Mr Corbyn might have taken another piece of clichéd advice for bands: it was all full of soul and feeling - from the heart.

Appropriately for a festival, there was a lot about love and peace and a better world. A burning sense of injustice, sure, but a steady rhythm optimism running through it - riffs on poetry, art and the wisdom of learning lessons from each other.

Warm and fuzzy or pie in the sky? Lying on your back on the grass, that sounds OK.

In one sense, it is a very old politics but it is the product of the new politics. Back in 2008, I frequently mused aloud that I knew the financial crisis would produce new political movements - I just couldn't tell what they would be - and 11 years later I have had my answer in spades.

Image copyright Getty Images Image caption Populist politicians like French President Emmanuel Macron have enjoyed recent success

Talk of populism has its place but the common thread which ties together Trump and Macron and links Italy's Five Star Movement to Corbyn, is a rejection of the existing political order and what's been tried before. A restless quest for something new, a hope for change.

That might sound weird when we have just seen a return to two party politics. But, while the label on the Labour bottle is the same, the contents are very different.

It is one of the many ironies of Brexit that Theresa May's analysis was probably spot on.

That the vote which turned the British political world upside down wasn't only about the European Union but about people left behind, missing out, ignored by an elite and frustrated. Her mistake - and ours - was to believe that she could capture that spirit.

Still, "Oooh Jeremy Corbyn" might be as good as it gets for Jezza. This could be peak Corbyn. What lies ahead is tougher - to convince people not only that he's a nice old geezer who's not the horned demon painted by the tabloids, but that he is a potential prime minister.

The Labour right's grudging acceptance that he had a good war has yet to translate into anything like helpful support. Many on his team want vengeance. His reshuffle buried no hatchets.

Neither right nor left of Labour seem to have heeded Paul Mason's acute analysis - which suggests giving the right the control of defence and security so the left can own the economy.

Image copyright Getty Images Image caption Theresa May has said she wants to reach out to the "just about managings"

The critical task is still holding together the fraying coalition at the heart of the Labour Party.

Mr Corbyn may be able to combine an appeal to partygoers in luxury yachts and people suffering in tower blocks, but it is much harder for him to reach those who bought their own council houses. Those white working class men on the doorstep shaking their heads and saying "not while he's leader" were not a myth.

Whenever the next election arrives, there will be more scrutiny of what he would be like as prime minister.

It is true the press have thrown everything they have to throw and the more over the top abuse has failed. But expectations were so low that it helped Mr Corbyn.

If, this year, people felt they could vote Labour as a protest, to dent Mrs May's predicted immense majority, they won't think that next time.

Then again, the Conservatives can hardly warn of the dangers of a weak government with a besieged leader with no authority trying to manage a party pulling in different directions on Brexit.

But Labour MPs will be the very last to breezily sing "Oooh Jeremy Corbyn". Capturing a sunny mood of righteous rebellion is very far from grasping the keys to No 10.

Chairman Mao said revolution is not a dinner party .

It doesn't even have its own VIP enclosure.