Was it really seven years ago? Lord Browne thinks that was when we last met formally - we've seen each other since at the occasional party or dinner - but that would seem about right: 2006.
Then he was CEO of BP. The following year, in May, he was gone; forced to resign after his attempts to prevent his gay relationship becoming public were revealed.
Back then, his office was a grand affair. There was a feeling when visiting him that the entire BP headquarters, indeed the whole company, had been crafted in his own image, from the frock-coated security guards to the vast, art-adorned lair that was his.
It was a sensation compounded by his love of giant cigars, which he would smoke while dressed in a handmade, usually blue, pinstripe suit.
John Browne had been CEO for eight years. Head of a hugely successful multinational, winner of a host of industry awards, including MT's Most Admired Leader on more than one occasion, a peer, and one of the highest paid executives in the UK, his sobriquet was the 'Sun King'.
Then, spectacularly, it all came crashing down. Today, there are no men standing guard outside his office, the Mayfair premises of Riverstone, the private equity firm he helps manage. It's smart but discreet; inside, there's some art - a framed Maria Callas disc, one or two other pieces - but nothing to detract from the quiet, functional air.
Browne is different too. His hair is greyer, the cigar has gone. But he looks good for his 65 years. The main change is that he can't stop beaming; his whole face is one big smile. He's much more relaxed than I can ever remember him being.
As well as Riverstone, which specialises in the energy sector, of which he is a partner and the US business's European head, Browne chairs Cuadrilla Resources, Britain's only shale gas driller - or fracker.
Cuadrilla, which is 44% owned by Riverstone, has been constantly in the news these past few months, as environmental campaigners have descended on its exploratory drilling operation in Balcombe, West Sussex.
It's got nasty, with 100 arrests so far. Fracking seems like a good place to start. Browne nods. It's as good as any. 'I don't think the opposition is justified but I'm not surprised.'
We, the public, he maintains, are being fed duff information about the dangers of fracking (injecting a mixture of sand, chemicals and water at high pressure deep underground to fracture shale to obtain gas). 'There's a movie, Gasland, which spells out the fears, but much of it, apparently, has been shown to be wrong.'
The fact is, he says, leaning forward and clasping his hands together over his knees in a familiar, earnest pose, 'fracking has produced an extraordinary energy revolution in the US'.
In the UK, Cuadrilla had to suspend operations in Lancashire because two earth tremors were detected. The company maintains they were too small to cause damage.
What about the US, where there have been cases of unlicensed drilling and, most serious of all, claims of water contamination? He's not smiling now.
'There is not one documented case where contamination has been caused by fracking. There may have been instances of bad well casings but they weren't fractured by fracking - the cement used to make them was not good enough. I acknowledge the reputation of fracking is mixed but the technology is proven and you can use it safely and well.'
No doubt, but the fracking process requires numerous chemicals, some toxic, such as hydrochloric acid, and the effluent can be contaminated with heavy metals, including mercury and lead. Then there is global warming.
Reports by the National Centre for Atmospheric Research in Colorado in 2011 and the UN Environment Programme in 2012 both found a significant risk that fracking could increase global warming because of the likelihood of increased leakage of methane into the atmosphere.
But, in August, research by the University of Texas found that methane gas emissions at nearly 200 fracking sites were within Environmental Protection Agency limits.
Here in the UK, he says, 'people took an instant dislike to fracking and, to be fair, there are worries, such as the effect it will have on the value of houses nearby. Hence, the debate with politicians and the people.'
But farmers and consumers, as well as homeowners, may have cause for concern. A US report has found fatal illnesses and deformities in livestock close to fracking sites in half a dozen states. Earlier this year, its author, controversial Cornell University professor Robert Oswald, called for a moratorium on UK fracking until tests show that it is safe.
Browne grins ruefully. 'There was a time when the Government was going to run the country on nuclear and renewable energy, and gas was going to go into decline. That's now changed. We need gas because it's the cleanest type of hydrocarbon and cheap - it's cheaper than nuclear or oil.'
That debate, he declares, is 'good to have'. But it's one he's determined to win. 'We will get there by persistence; there will be protests, there will be running battles, but the policy-makers are persuaded.'
Let's return to BP. There, he tried to refocus the company, to make it take renewables seriously via his 'Beyond Petroleum' policy. Since then, under Tony Hayward and now Bob Dudley, that shift in emphasis appears to have diminished.
He's not keen to discuss his old firm at all. 'I have nothing to do with BP other than social contact. I'd not been back for five years until I was invited in for lunch by Bob. I saw the general counsel and chairman while I was there and, apart from bumping into people at parties, that's it.'
BP is a robust company and it's getting on with it, says Lord Browne. Photo by Harry Borden.
He will not be drawn on what he thinks of the company now. 'BP has suffered a gigantic, multibillion-dollar body blow (the Deepwater Horizon oil rig disaster). But it's a robust company and it's getting on with it. Bob is very calm - he was my executive assistant in 1999-2000. After we took over Amoco he was the first Amoco person to work for me in my office.'
It would be 'inappropriate for me to comment on BP. It was an important part of my life from 1966 to 2007. We did some great things, but we did not do everything well. If I claimed it was all good I would not be telling the truth.'
He hesitates. 'I opened up new vistas, we employed a lot of people, we launched a flagship policy, Beyond Petroleum, we expanded so a two-pipeline company became multi-pipeline, and we went into Russia, which in the end turned out to be good ...'
And there was bad: the Alaska pipeline spillage in 2006 and Deepwater in 2010, which it has been claimed were caused in part by cost-cutting when he was in charge. His contempt for the accusation is obvious. He grimaces and shakes his head. He's dismissive. It's not worthy of comment.
However, the US Oil Spill Commission (OSC) set up to investigate the Deepwater disaster, in which 11 died, found in its 2011 report that officials had made 'a series of decisions that saved BP (and its contractors) time and money - but without full appreciation of the associated risks'.
In the 2005 Texas City BP oil refinery explosion 15 died. The same report found: 'Cost-cutting and failure to invest in the 1990s by Amoco (who (sic) merged with BP in 1998) and then BP left the Texas City refinery vulnerable to a catastrophe. BP targeted budget cuts of 25% in 1999 and another 25% in 2005, even though much of the refinery's infrastructure and process equipment were in disrepair.'
In November 2003 a gas line ruptured on BP's Forties Alpha platform in the North Sea. Fortunately, there was no explosion; however, BP was fined $290,000 for allowing pipes to corrode. BP engineer Oberon Houston, interviewed by the OSC for its report, said BP focused heavily on personnel safety and not on maintaining its facilities.
He added that BP was preparing to sell the depleted field and was running it at minimum cost: 'The focus on controlling costs was acute at BP. They just go after it with a ferocity that is mind-numbing and terrifying. No one's ever asked to cut corners or take a risk, but it often ends up like that.'
It's not surprising that Browne prefers to leave BP alone. 'You have to understand that on 1 May 2007, life changed for me. My world crashed, everything changed overnight.'
After an attempt to stop the Mail on Sunday outing him as a homosexual, Browne faced the threat of contempt of court charges over a written court deposition about how he met former partner Jeff Chevalier (the charges were later found to be inappropriate). The charges were not brought, but he was forced to resign.
So all he will say on Beyond Petroleum, for example, is that when he was at BP, lots of experts agreed renewables were the way forward. 'But BP has since concluded it is not a priority and adjusted accordingly.' He shrugs. That was its decision. If he's hurt, he is not letting on.
It must have been terrible, his fall? He nods. 'The most important thing I found afterwards was people. Some were supportive, others not. Some did not talk to me at all. Early on, one chap asked what I was doing. I said I was retired - this was before Riverstone. He said: "That's not interesting. In my view, people are only as good as the position they hold."'
Adds Browne: 'That's such an awful view. It's as if you've nothing else to offer.'
So what do you do when that happens? He smiles. 'What you do is you start again. For three weeks to a month afterwards I was low. Then you build up, step by step. On 1 September 2007, I agreed to be a partner in Riverstone in London, and then I had to find an office and furniture and hire people. It was like a start-up, it was great.'
He wrote a book about the experience, about his career at BP and his sudden demise, Beyond Business. That was clearly cathartic. So too, it seems, is lending advice to people in the same boat. He laughs, but he's become a sort of agony uncle for others in crisis.
What does he say to them? 'I always say 'go forward. History is interesting but you don't live it. You've got to live the future. You must work out what you want to do and get on and do it, but build it up slowly, bit by bit.'
He adds: 'It's a huge change from being the leader of a company like BP to being just you.' But he's done well, I say. In fact, he appears happier now. 'It's true, I am happier. I'm happier as well because I came out.'
He laughs again at the madness, of losing BP and stopping living a lie. 'An awful lot changed in those 24 hours.' As for today, 'Now I like what I do, I like the mix.'
In addition to Riverstone he's close to the Government. He wrote a report on university funding and he's played a leading role in recreating company-type boards in each department of state. He's chairman of the Tate trustees and he's writing books - he's just produced another, Seven Elements, a look at elements that have changed the world for good or bad, from carbon to uranium.
He's writing a third. The Glass Closet about homophobia in the workplace. 'We need a more positive approach to the way we treat homosexuality and that has to come from the top,' he says.
'It's important we hear about discrimination and the effect it can have. We have to make the world a safer, more equal place for gays, and for women.'
He admits to regret at keeping his homosexuality hidden for so long. But he adds in the same breath: 'Would I have got as far as I did at BP if I'd come out? I don't know. As it is, I've been able to enjoy it all - a terrific career and, now, being out.'
It's strange that Browne today is more willing to discuss his sexuality than he is business, but that's where we are. Riverstone is now the no-go area. What does it do? 'It invests in energy,' he says.
And that's all he volunteers. 'We will not talk about it,' he adds firmly. In fact, Riverstone is the world's largest renewable energy fund and the firm has $26bn in equity capital across seven funds.
But Riverstone has established a new energy investment vehicle, listed on the London stock market? No matter, it prefers to maintain a wall of privacy.
The backers of the new venture, Riverstone Energy Ltd (REL), are institutions and funds controlled by wealthy families who eschew publicity. What is known is that Riverstone plans to raise up to £1.5bn with the new vehicle.
He's more optimistic about energy than he's ever been. 'There's plenty of oil and gas to be found; new technologies are coming through that will help us find more. I am confident we will never again discuss "peak oil" or a gas shortage.'
As for himself, he has no plans to retire. 'I'm 65, already beyond retirement age.' As well as exploiting the openings in energy via Riverstone, he's got yet another book to finish. 'It's about how business can become a force for good in society.'
Away from work, he divides his time between London and Venice. 'My country house is in Venice,' he says, his eyes twinkling. He knows what he's just said.
His contentment is palpable. 'I suppose 2007 was salutary. The fall taught me a lot, about banality, about our obsession with the trappings of business success and position. It made me reflect on who I was and what I wanted to do.'
There's a theatrical pause. 'Mind you, I wouldn't have chosen that particular technique for changing my life.'
And he breaks into another of those smiles.