With sun already dipping below the horizon, the shadows of night are being held at bay by the bright lights of the store fronts of Knightsbridge and today's round of promotional duties for Roger Waters are nearing the finish line.

"As we're coming to the end of the day," he chuckles as he reaches for bottle of chilled white wine. He pauses momentarily to survey the bottle's half empty contents: "That's not bad - that's since 12 o'clock." This, then, must be one of the very rare occasions that the erstwhile Pink Floyd leader is doing anything by halves.

The Quietus is meeting with Waters to discuss the release of his latest project, Roger Waters: The Wall, a CD and DVD document of his globe-trotting, three-year world tour revival of Pink Floyd's 1979 album - the highest-grossing tour of all time for a solo artist. Written and directed by Waters and Sean Evans, the film not only captures the artist in concert and all the epic grandeur that surrounds it, but it also concerns itself with Waters attempting to make some sense of the horror and brutality of war as he embarks on a personal quest to visit the resting places of his grandfather and father who were killed in the First and Second World Wars respectively.

Contrary to popular belief, the Waters that The Quietus meets is far from the bad-tempered misanthrope that is frequently portrayed elsewhere. Instead, he's talkative, articulate and passionate about his art and the worst aspects of human nature that inspire it.

This is the third incarnation of The Wall. Why did you return to it and would you have done so if you had known that it would take such a chunk out of your life?

Roger Waters: I went back to it because I had re-discovered a love of performing. So after doing the Dark Side Of The Moon tour and after doing the In The Flesh tour, I felt that maybe I could do one more tour, but what should I do? The Wall was an obvious choice if I didn’t have anything new in the pipeline, which I hadn’t.

I talked to [rock tour designer] Mark Fisher about it and he said, “If you’re going to do The Wall again, then you’ve got to build a physical wall like you did it first time round” and I went, “But Mark, if we did, we won’t be able to make any money!” He said, “No, it’s different now. People pay more for tickets” so I went to get the numbers crunched and realised that we’d have to play a lot of gigs before we broke even but I said, “OK, let’s do it!” And that was the start.

What’s particularly interesting about this production is that the narrative thrust has changed from that of the alienated rock star to a message of anti-war. Why did you do that?

RW: Because I’m even more vehemently anti-war now than I was when I first made the record. And I’m far less obsessed with the travails of the poor, fucked up, miserable little Roger from all those years ago that we talk about in ‘Mother’. And I’ve come to realise over the years what a good metaphor and allegory The Wall is for the current political situation and what a malign influence these barriers that we construct are.

The story that’s being sold to “the great unwashed” is that, certainly in the United States where I live, we are at war and that we are in a permanent state of war and we are going to be for as long as anyone can see because we are fighting a war against “terrorism” and also “terrorists”, and “terrorists” are anybody that we don’t agree with. About anything. And we, the great American nation, decided that we’ve got 138 military bases around the world and we’ve now figured out that we can buy these drones from the Israelis, and we’ve decided that the way to proceed is to use this new technology to go and kill anybody that we don’t like or who disagrees with us or who we might perceive as making an existential threat. Obviously they’re not an existential threat against the United States of America or anywhere else in any serious or legitimate way; it’s an exercise in control.

Now, this is how you control your domestic population – by making people afraid and by identifying an enemy. It’s funny that with this whole thing of The Wall, to me and most thinking people anywhere in the world, is that moronic Donald Trump is talking about building a wall across the Mexican border. And you think, he’s not serious? But he is serious. And what a good thing that would be for them. It’s an exercise in control; all you have to do is scare the shit out of your domestic population and you can get them to do anything you want and you can carry on fleecing them rotten until you’ve destroyed society completely and they get very rich in the process.

As Smedley Butler said, ‘War is a racket.’ He was the most decorated soldier in the history of the American military. He fought in wars all over Central and South America and he spent his entire career in the marines. He ended up as a general and he retired in 1929 and shortly after that he wrote a famous essay called War Is A Racket.

The film also deals with you going back to the burial place of your grandfather who was killed in WW1 and where your father died in WW2. What were you hoping to find on a personal level?

RW: Two things: one, to stand on that spot [where my grandfather is buried] with my children – his great-grandchildren – because I’d never been and to say, ‘This is were your great-grandfather lies. This is what his name was and who he was. He was a coal miner from the village of Copley in county Durham and this is where he’s buried.’ As I say in the film, it’s been an ambition of mine to stand there with my children. It was a very moving moment for me to be there with them.

With my father, I’d never been to the memorial garden. I’d been to Anzio before but because we’d done all that, there was this old bloke who lives to the east of Rome on the coast and he’s an ex-Sherwood Forester and he was fighting about a mile away from where my father was killed that day. He saw me on TV in Italy when we were filming in Cassina and he was interested in it. His name is Harry Shindler and he’s now 94-years-old and he thought to himself, 'that’s interesting', and he [Waters] needs to hear the end of his story so I’ll do some research and find out where his father actually died.

And he did! He found exactly where my father died by going through regimental war records and a ton of research and he’s become a good friend. He then persuaded the town council in Aprilia – the town that’s nearest to where my father died – to build a monument to him, which exists now and is in the playground of some local elementary school. That’s pretty amazing. It’s a simple obelisk and about nine-foot tall.

We had some interesting conversations about it, like what to write on it. And he said, ‘Alright Roger, we’ll write, “2nd Lieutenant Eric Fletcher Waters and all the other Allied fallen”’ and I said, ‘You’re not putting the word “Allied” in there.’ And he said, ‘Why not?’ and I said, ‘Because this isn’t about nationalism. We can put “all the fallen” but we’re also including the fucking Germans as well. I’m not going to go, “Ra-ra!” There are no Union Jacks around this. You can have a dove and the rank I can deal with.’ And it says on the memorial, ‘Ashes and diamonds/Foe and friend/We’re all equal in the end.’ I get slightly choked up thinking about it. So that memorial for my father has that quote on it from one of my songs [‘Two Suns In The Sunset’] written on it.

Could you talk me through ‘The Ballad Of Jean Charles de Menezes’? What attracted you to that subject?

RW: After we decided to do the show we decided to use the idea of fallen loved ones through it so we needed stories and pictures so [the film’s co-director] Sean Evans and I started a website specifically for people to write in and send us information. We got thousands of people sending us in photographs and information. With Jean Charles de Menezes, his family sent in a picture. Obviously I already knew the story because he was murdered just down the road from here. His family came to the show in Porto Alegre in Brazil and I met them. They were very worried about the fact that the British government never apologised to them. Not a word. They didn’t even say, ‘Sorry, we made a mistake.’ And his family kept saying, ‘Why? Why not? Why wouldn’t they apologise?’ I looked into it and they were quite right.

In ‘Another Brick In The Wall Part 2’ [in the live shows] we used to have Dave Kilminster playing Dave Gilmour’s solo, then Snowy White playing his own solo and then my son, Harry, playing a Hammond solo. After we’d done about 50 gigs, I went, ‘You know what? That’s a solo too far. It’s wrong and I lose interest in it.’ And I thought, maybe I could write a Jean Charles de Menezes song and put it in that one minute there. So I took the click track with me back to the hotel so it’s exactly the same tempo as ‘Another Brick In The Wall Part 2’ and I figured out how to write a song that lasted exactly the right amount of time instead of that Hammond solo. I went and taught it to the band and then we rehearsed and I said, ‘Yeah, that’s what we’re going to do.’

Something occurred to me watching the film. You have an all-new line-up of musicians re-creating the 1979 album and it’s an all-new production. Could The Wall continue as a production that has revivals like West End plays do long after we’ve gone?

RW: Yeah, there’s no reason why not if people would go. I’ve often thought about that, that people could do it. Anybody could do it. It’s not a big deal. I mean, if the fucking Australian Pink Floyd can bosh around the world for 20 years or so selling out 15,000-seat arenas then there’s no reason why this shouldn’t do.

Do you think that rock music is still a viable medium for political discourse? I interviewed Bob Geldof a few years ago and he was adamant that it’s had its day.

RW: Well, he was never political anyway, was he? ‘I Don’t Like Mondays’? What are you talking about? Did The Boomtown Rats do anything political? If they did then I don’t remember it. It’s none of his business really. I mean, he can be – and quite rightly – a spokesman for Live Aid and Live Earth and Live This and Live That and Live The Other because he was a rock & roll activist on behalf of the poor of Africa for all those years - and hats off to him - but in terms of writing songs that have some kind of political element to them, I don’t think he has a dog in that race.

But yes, I do view it as a viable medium. It’s funny, I did a little gig with G.E. Smith the other day and I played a couple of new songs with him on a couple of acoustic guitars and they’re very, very political and I was thinking that the measure of proper song – and not even just political ones – is that you’ve got to be able to play it on a guitar or piano and be able to sing it and it has to live like that to be good. Having done that gig I realised that I could say to G.E. or a couple of other people, ‘Well, OK, I’ve turned into John Prine and we’re going to do this all over the world and fuck the show. Let’s just play in smaller venues and do this.’ And I probably could but I’m still wedded to the big rock theatre, partly because I invented it! [laughs]

You’ve mentioned elsewhere that you have a new concept ready with regard to your next album. Given that you’ve been involved with some of the biggest-selling albums of all time, to what degree do you think that – on an artistic level – you’re in competition with your younger self? Can you achieve anything like that again?

RW: Well, obviously I can’t. I can in terms of the work and there’s no reason that I can’t produce another work that’s very, very important. But because the marketplace has been hi-jacked by the pirates, no one can own intellectual property anymore so you can’t really have records anymore. As soon as a record comes out, it will be stolen immediately. Immediately it’s gone! The second it goes out, it’s stolen! God knows what you can do about that but I fear for the world that does not reward songwriters and musicians for plying their trade because it’s been a very useful adjunct to all of our lives and it’s going away. You’ll have nothing left but Simon Cowell and Kanye fucking West and what an awful world that will be.

But I don’t feel as if I’m in competition with myself; not at all. Interestingly enough, I think I’m taken more seriously now than I ever have been in my life. I feel I have the potential to reach an audience beyond anything I can imagine. Obviously it’s been a tricky kind of 30 years since I left Pink Floyd because people were very confused; they had no idea who I was and quite a lot of them still don’t. There are so many people out there who think they are fans of Pink Floyd – and certainly the work I did in Pink Floyd – who are still furious that I left.

Roger Waters: The Wall two-disc Special Edition is out now on DVD and digital download. The soundtrack is available on CD, Vinyl LP and digital download from November 20