FROM the outside, Tony Blair’s office in central London looks completely anonymous; a wall of frosted glass with no signs, just a small flickering intercom.

On the inside, the grand-sounding Institute for Global Change has the feel of a five-star Middle Eastern hotel; upmarket furniture, modern paintings of what look like Jerusalem, chrome and glass and, of course, photographs, many of the former Prime Minister with the likes of Barack Obama and other world leaders, past and present.

The receptionist greets me with a smile and I’m ushered up the lift, past a bank of aides tapping earnestly on their keyboards, to a grand reception room with sofas and a desk.

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Mr Blair breezes in, apologises for the delay, saying he has just been on an important international call.

The air of calm authority is still there, along with the receding hairline and wrinkles. The former Labour leader celebrated, if that is the right word, his 66th birthday on the very day of the 20th anniversary of the first elections to the “reconvened” Scottish Parliament. But the energy persists.

Needless to say, the madness that is the Brexit process is never far from his lips.

He says: “Wherever you are in the world today and you meet political leaders, there is a conversation that is a kind of amusing competition as to whose politics is crazier, but I have to say we are Champions League… we are the Barcelona or maybe the Liverpool of the pack.”

Looking back, I recall how he once admitted to never being a passionate believer in devolution and, indeed, once described creating the Scottish Parliament as a “dangerous game to play”.

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But he insists he was “intellectually and politically persuaded” of the case for Scottish devolution.

“I was always worried as to whether devolution would be the way of keeping the UK together or the slippery slope to breaking it up,” he says.

“But devolution is in place, the Scottish Parliament does function, Scottish politics does function and Scotland’s still in the UK and, on the evidence of the last few days or few weeks, there is not a groundswell of opinion to shift Scotland out of the UK.”

I mention how it was suggested he “wobbled” over setting up Holyrood and was taken aside by John Smith’s widow to insist devolution was “John’s unfinished business”. Mr Blair shifts in his seat and remembers how there was a great deal of anxiety about how he wanted a referendum on the subject.

He says: “I had studied the history of devolution – which people had been striving a hundred years for and had not delivered – and had come to the conclusion that the biggest threat to devolution would have been in the House of Lords, where at that time – remember, this was before our reforms – there were the hereditaries, who were all sitting there; so the Tories had an in-built majority.

“The Tories were essentially against devolution and I knew the only way of heading off that House of Lords rebellion at the pass was if you could say to them: ‘I’m sorry, this is the settled will of the people’.

“I remember at the time all this bizarre stuff, with people saying you’re betraying the Scottish people by having a referendum, and I would say if people are not prepared to vote for it, I don’t see how I am betraying them, but this was part of politics. That was the origins of ‘was I wobbling or not’.”

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Moving to politics today, Mr Blair notes how the tension over constitutional change was not unique to Britain.

“It’s a tension you see all over the world, where there is an uneasy constitutional relationship with secessionist tendencies. But, having said that, the leap to independence is quite large and my sense is – other than if Brexit really upsets the dynamic – there is still a functioning majority for Scotland staying in the UK.”

When I suggest if the SNP cannot secure independence in the midst of a tumult like Brexit, then it might be difficult to see when they could realise their goal, Mr Blair replies: “I will get into trouble with Nationalists when I say this, so let me choose my words more carefully than I sometimes do: a lot of the Nationalists are people who are inspired by genuine views of social justice, they are not small-minded Nationalists at all; someone like Nicola Sturgeon is plainly not a small-minded person, on the contrary.

“But I just think when you take a big picture view of the world, and you see the geopolitics of the world is changing in the 21st century, it doesn’t make sense, in terms of self-interest, to break out of any large collective grouping of which you are part, provided there is at least a reasonable degree of cohesion in that grouping.

“The reason it’s foolish for Britain to leave Europe is for geopolitical reasons that also make it not sensible for Scotland to leave the UK.

“That doesn’t mean to say that people who want, particularly the Scottish Nationalists who want to leave the UK, are doing it for petty reasons – I don’t mean that at all.

“But the biggest change in my children’s lifetime is going to be the rise of China and the West needs to just wake up to what this means.”

Mr Blair adds: “This is where your alliances matter. One of the things that’s so depressing about the state of British politics at the moment is that people don’t see this big picture about the way the world is changing and realise therefore that at every single level your alliances become important.

“Scotland’s alliance with England is important. Britain’s alliance with Europe is important. Europe’s alliance with America is important. Because you are faced for the first time in modern times power is shifting east [to] China and India. This is a vast geopolitical change.

“We are more interconnected than ever before and therefore any alliance you have increases your own power.”

Mr Blair makes very clear he does not believe in allowing the First Minister a second bite at the independence apple.

He says: “First of all, I don’t think we should have one unless there really is a big groundswell of opinion for it and I don’t see that.

“Secondly, to be brutally frank about it, the last thing we need at this moment is another huge dose of constitutional uncertainty; we really would start to damage ourselves fundamentally as a country.”

But I point out that, in the interconnected world he refers to, surely the Scottish Nationalists have a point; that if the UK leaves the EU, it would make sense for Scotland to leave the UK to rejoin the EU?

He does not accept the argument.

“I would still want Scotland to remain with the UK; be in no doubt about that,” says Mr Blair.

“But it’s a statement of common sense that if Scotland is in favour of Britain remaining in Europe and Britain leaves Europe, you’ve obviously got another argument.

“I know when I say this some people in Scotland on my own side say: ‘Oh God, you can’t say that,’ but it’s a statement of the obvious. If you’re a Nationalist, it gives you an additional argument; which is another very good reason by the way for not doing Brexit.”

I suggest he is taking a contradictory position by suggesting the last thing Britain needs is another Scottish referendum, but he is in the same breath proposing another one on Brexit.

Mr Blair holds up his hands and says: “I wasn’t in favour of having the referendum in the first place; I wouldn’t have had the referendum on Europe. I’m extremely nervous of referendums for all sorts of very sensible reasons.

“But if you are going to change this decision taken in principle by referendum, then I don’t think you can do that other than by another referendum.

“But if there is one thing all of this has taught us it’s the danger of plebiscite democracy over parliamentary democracy.”

Asked if, on the back of the Tories’ turmoil, the election of someone like Boris Johnson could be a threat to the Union, Mr Blair says: “It’s a problem if the Tories become an English Nationalist party, which some of them undoubtedly want despite the fact that a lot of them talk about the Union the whole time.

“Of course, for Northern Ireland but for Scotland [too] it’s obvious, if the UK is led by someone from that English Nationalist perspective, then, of course, this would be an additional string to the bow of Nationalists, but that’s why it is important it doesn’t happen.”

As the prime minister who led the government that brought in devolution, he is asked if it has met his ambitions.

He replies: “Yeah, but 20 years is not that long in the history of the constitution. On the whole, devolution has worked better than most people [would have thought].”

He adds: “When people look back on the [New Labour] government they will realise in constitutional terms we were probably the most radical constitutional change-makers of any government in modern political history by a significant margin.

“I would consider devolution an achievement, yes, because in these times to try to change the constitution in radical way and keep people together was an achievement.

“My son [Leo] is studying politics now and a significant part of the study is about the constitution.”