Stuart Hall is as a God on the landscape of the left. Not in the hyperbolic sense, of the respect in which he is held: rather, that any conversation, be it about multiculturalism or feminism, Karl Marx or the free market, as soon as it reaches a level of any depth, it will come back to his ideas (I nearly just capitalised that H).

Hall arrived in Britain in 1951 and went to Merton College, Oxford, on a Rhodes scholarship. "Three months at Oxford persuaded me that it was not my home. I'm not English and I never will be. The life I have lived is one of partial displacement. I came to England as a means of escape, and it was a failure." He says all this with an amused look, as if to say that his displacement hasn't dented his happiness, and his failure seems, if anything, to have tickled him.

He has lived here for 60 years, and is married to Catherine Hall, a professor at UCL. To sit in his Hampstead kitchen, with the sun streaming in, the day before his 80th birthday, I have this surreal sense that I'm looking at an ur-academic, totally uncompromised, fulfilled, successful, the kind of academic John Updike might have written, when he was young. Hall says, again amused: "I was going to be – dirty word – an intellectual. Academia was just how I made my money."

He became one of the seminal figures of the New Left Review in the 50s (alongside Ralph Miliband, whose rolling or otherwise in his political grave, let's leave aside); it is interesting to note that the memorable ideas from that publication, into the Thatcher years and beyond, were often Hall's coinage. Beatrix Campbell, in a letter to the London Review of Books this January, mentions Thatcher's "retrogressive modernisation", as described by Hall. But his greatest mark in terms of popular thinking was in the field of multiculturalism, as a faculty member and later director of the Centre for Contemporary Cultural Studies at Birmingham University.

Until very recently, Hall's articulation of the multicultural society looked like the one fixed advance of the 60s, the one improvement that no amount of political rhetoric or social polarisation could undo. He mildly rejects the idea that academia was the engine of the new world order. "We drew the line in the 60s. We were here. They were there. It wasn't going to look like Dunkirk. It was never going to look like that again. I think some advances were made academically, but it was more what I think of as a multicultural drift, just having them [people from other cultures] around, they weren't going to eat you, they didn't have tails. The smartest guy in the store is probably black. You turn on the television and the guy singing is probably black. That mattered a lot in accustoming people to think about it."

And he still maintains that this country, which has adored Bob Marley for three decades, is a very different place to the one he arrived in. And yet, he says, "I'm more politically pessimistic than I've been in 30 years."

This pessimism is not down to the failure of multiculturalism, or rather, that speech last year in which David Cameron claimed it had failed – Hall takes a benign, if dismissive, attitude to Conservative posturing here, commenting mildly that Cameron is talking about equal-opportunities legislation, as he perceives it, rather than multiculturalism as part of the culture. No, it's the state of the left that strikes him as the most problematic. "The left is in trouble. It's not got any ideas, it's not got any independent analysis of its own, and therefore it's got no vision. It just takes the temperature: 'Whoa, that's no good, let's move to the right.' It has no sense of politics being educative, of politics changing the way people see things."

The examples of this are everywhere, but take as the most pressing the case of the NHS. "How can millions of people have benefited from the NHS and not be on the streets to defend it? Come on. The NHS is one of the most humanitarian acts that has ever been undertaken in peace time. The principle that someone shouldn't profit from someone else's ill health has been lost. If someone says an American health company will run the NHS efficiently, nobody can think of the principle to refute that. The guiding principles have been lost." There was a study recently investigating why America, which spends more per capita on health, has worse outcomes, and the answer was quite clear: when there is a profit motive, the rich are overinvestigated, and the poor are undertreated. People die needlessly.

So there's quite a sound pragmatic argument against private involvement in health, but Hall's is a blistering moral statement – who would profit from someone's ill health? What sort of person would that be? Would you trust them with your budget, let alone your health, or the health of a loved one? The moral case is not being forcefully enough put; indeed, it is not being put at all.

Being human and all that, and 80, Hall has observed the NHS at close range recently; following a diagnosis of renal failure, he spent seven years on dialysis, but by that time, "it's killing you and keeping you alive at the same time". This was a very profound experience. "It gives you a different conception of yourself, a different conception of yourself in relation to others. Your wife becomes your carer. For God's sake!"

But, of course, it has deepened his political identity as well. "I've always known in my head I'm not an island, but it really came across. It's not just the kidneys – I could give you a litany of things that are wrong with me. I couldn't go two days without someone coming in to help me. [Richard] Titmuss called it the gift relationship – you throw your bread on to the water, you don't know who will pick it up, you don't know if you're going to need it later, you just give it because you have it. That's the opposite of exchange value. It has no value.

"You recoup nothing. I've always thought the ego, Adam Smith's selfish individual, was wrong. The outside world gets into our heads, there is a constant dialectic, it is ineradicable. So we have to forge consanguinity. I've always known that, but of course if you're ill, it comes through much more. Have you any idea how much dialysis costs per session? Do I believe in a public health system? I sure do. With bells on."

It is this failure of the Labour party to make a strong moral case, to dare to inspire people, that Hall takes as the main threat to the political landscape. He was impressed by the part of Ed Miliband's conference speech about business "predators", but he doesn't have this modish interest in the evils of business, big or small. He reserves his analysis for the weaknesses of mainstream politicians, though not vindictively; rather out of an apparent belief that they could be much better.

We talk briefly about David Lammy's comments about hitting children, this new articulation of multiculturalism where diversity is ranged against liberalism, so that the very liberal voice which should be celebrating difference is actually thwarting it with namby-pamby legislation. "I think he's playing to the gallery. He's not talking about multiculturalism. He's saying, 'Get back to the good old verities, you can't go out because you can't go out because you can't go out.' It's old-school authoritarianism. He's the person who knows how Tottenham feels. Politicians always think they know what people feel. It's a fallacy, because there is no such thing as 'the people'. It is a discursive device for summoning the people that you want. You're constructing the people, you're not reflecting the people."

While we are on the racial flashpoints of recent weeks, what does he think of Diane Abbott, and the "tactics as old as colonialism" furore? Laughingly, he doesn't want to go anywhere near this subject, but throws in: "It was just incredibly bad timing, and a lack of care in formulating the argument." I suggest, here, that the mainstream has got into the habit of appropriating the sensitivities of the minority, as a way of making them seem ridiculous. So you'll get home-counties Tory MPs claiming to be offended by Abbott's "racism", when of course they aren't offended, they're just trying to discredit the whole idea of racism causing offence. "And you say you're the optimist!" he says. "Look, Gramsci, the Italian Marxist, believed in pessimism of the intellect, optimism of the spirit. You must look at what's happening now. If it's unpropitious, say it's unpropitious. Don't fool yourself. Analyse the conjuncture that you're in. Then you can be an optimist of the will, and say I believe that things can be different. But don't go to optimism of the will first. Because that's just utopianism."

Naturally, we arrive at the riots of the summer, the place where the austerity, these so-called "failures" of multiculturalism, the absence of politics, all meet, in Foot Locker, of all places. "The riots bothered me a great deal, on two counts. First, nothing really has changed. Some kids at the bottom of the ladder are deeply alienated, they've taken the message of Thatcherism and Blairism and the coalition: what you have to do is hustle. Because nobody's going to help you. And they've got no organised political voice, no organised black voice and no sympathetic voice on the left. That kind of anger, coupled with no political expression, leads to riots. It always has. The second point is: where does this find expression in going into a store and stealing trainers? This is the point at which consumerism, which is the cutting edge of neoliberalism, has got to them too. Consumerism puts everyone into a single channel. You're not doing well, but you're still free to consume. We're all equal in the eyes of the market."

And this is the most pessimistic of all his ideas: that three decades of neoliberalism have got into people's consciousness and infected the way young people respond to poverty just as they have neutered the way politicians express themselves. "I got involved in cultural studies because I didn't think life was purely economically determined. I took all this up as an argument with economic determinism. I lived my life as an argument with Marxism, and with neoliberalism. Their point is that, in the last instance, economy will determine it. But when is the last instance? If you're analysing the present conjuncture, you can't start and end at the economy. It is necessary, but insufficient."

In this present conjuncture, though, he sees everywhere the hangover – indeed, the ongoing orgy of an essentially economic agenda. The left is faltering because it can't realistically say it didn't continue what Thatcher started. The institutions of the old welfare state have already been "hollowed out. This is what Blair discovered – you don't need to have a fight about privatisation, you just have to erode the distinction between public and private."

But it is that lifelong argument against economic determinism that makes me doubt Hall's commitment to a pessimistic view. That's probably unjust, I'm sure he is a pessimist of the intellect; but his life's work has been to give intellectual expression to the possibility of something better. It would take more than a financial crash, more than three decades of neoliberalism, and so much more than a Cameron-led coalition government to eradicate that.