Denis MacShane was the UK's Minister for Europe under Tony Blair, and one of the most pro-European politicians of his generation - yet even he fears Britain is heading for a 'Brexit'.

During a public debate at the Bozar concert hall in Brussels organised by the French weekly l’OBS, and the Belgian dailies De Standaart and Le Soir, the author of Brexit: How Britain Will Leave Europe, tells Matthew Tempest why.

Let’s start at the end and work backwards – what’s your prediction for the referendum?

I am the official Cassandra for the European movement – I believe that it will be very difficult to turn around 20 years of Conservative, business and mass media hostility to European integration. And when given a chance in a populist plebiscite people will want to give the elites a kicking, Europe a kicking, maybe Prime Minister Cameron a kicking over tax credit issues.

And I have a very strong fear we’re going to vote ‘Out’.

Well, put a number on it. How close do you think it might be?

I think it will be close. I think it will be close either way. And as a result it won’t resolve anything. If we stay in by the skin of our teeth thanks to voters in Scotland, all the eurosceptics will cry foul. If we vote ‘out’ thanks to English eurosceptics the Scots will cry foul and organise their own vote for independence.

And if we vote ‘out’ there will chaos and confusion over the terms of our leaving, the terms of our continuing relationship in terms of economically, trade, supervision of our financial services with the 27 other member countries that will last years.

I would hope if we voted ‘in’ it would finally say to Mr Farage and William Hague and all the other Eurosceptics ‘game over’, just as the decision to vote ‘in’ in 1975 should have been the beginning of Britain engaging seriously in Europe but it wasn’t. Within five years leaving the EC, as it then was, was the official policy position of the Labour party, and in the manifesto of 1983.

So the idea that a plebiscite ever solves the European question is false. Only leadership and telling the truth about Europe can achieve some of that.

Isn’t that also the lesson of the Scottish referendum in a way, in that even though it was narrowly lost by the nationalists, it certainly hasn’t killed it off?

No, a plebiscite solves absolutely nothing at all. It’s spasm, emotional, politics.

Is there a danger it could end up being a referendum about migration, especially in the wake of the Paris attacks, rather than about the EU institutions?

Enormously. The Daily Mail’s front page today (19 November) is 53% want to ban EU citizens’ from living permanently in UK. Well, imagine if Spain started saying that to the Brits who live in Spain. So immigration is a huge issue, and it is true that over the last 25 years we have seen the biggest people movement in Europe probably since the end of the Roman Empire. We’ve seen so many incomers. Not just in Britain, in all countries. There are 500-800,000 Romanians living in Italy and Spain. There’s half a million Albanians living and working in Greece. You then add in the new religions that are coming in, you add in the new ethnic groups that are coming in from Africa and the Middle East, and it’s a time of immense confusion. And then, put into that, the absence of growth – I mean, jobs are the biggest integrating factor in any immigrant or refugee group, and we don’t have enough jobs in Britain and the rest of Europe to absorb all these people, especially in places like Spain and the Balkans and Greece – where unemployment’s running at 40-50%.

One final prediction – when do you think the referendum will be?

‘If it t’were done, t’were well t’were done quickly’ – I’m sure David Cameron has read Macbeth. I think it’s a terrible personal decision for him, I have considerable personal sympathy. I think he has reduced all the old Tory demands into the bare minimum that are manageable in terms of what the rest of the EU can concede to Britain.

This has never been a debate about what 27 other member states and the Commission can give to Britain. It’s always been about the Conservative party, about the offshore-owned press and about the culture of anti-European populism that has developed in the past 15-20 years and Mr Cameron has yet to turn around to his own party and say, "It’s game over, we have to stay in the EU."

I don’t think putting it off will change anything. He must feel a bit like General Eisenhower, deciding 'Do I go on June 6th, 1944? Or will there be a storm in the Channel?" It’s a horrible choice for him. But I personally do not think that’s there much to play for in putting it off. To stretch it into 2017, and mix it up into the French and German elections, seems to me to be insane.

But, frankly, he has not yet shown any courage in turning to his own ministers, in turning to Boris Johnson [Conservative Mayor of London] to say "The future of Britain depends on staying in Europe, and the future of the Conservative party, as the most successful governing party that Europe has, and that Britain’s ever had, depends on us now – like with the Corn Laws, like with votes-for-women, like with Irish independence, like with votes for Catholics – putting to one side our old prejudices and saying the national interest demands that we stay in Europe. "Full stop, not with the ‘buts’ and ‘ifs’ and ‘if Europe changes’ and ‘if Europe becomes more like us.'

I was going to ask you about Boris Johnson. Do you think he could be the game-changer? Do you think he would have the motivation, or the courage, to come out as an ‘outer’?

I don’t know. Let me be honest, and I’m quoting here James Lansdale, fellow old Etonian and now BBC’s deputy political editor, and Lansdale did a little ditty about the lies that Boris told as the Daily Telegraph’s Brussels correspondent. Not criticisms of Europe, downright untruths. And that has been his conveyor-belt to fame and popularity for the last 25 years. So asking Boris to change his anti-European spots is difficult.

He’s obviously got a very hard personal question, or decision to take. If he announces he’s in favour of Brexit, he automatically becomes the leader of the campaign, and sweeps Farage and all the others into the gutter, and becomes the most prominent British politician in recent years. Because if Brexit happens, David Cameron has to resign..

And [Chancellor] George Osborne, too?

And Osborne. They both have to go. And Boris scoops the pool, to become prime minister. So if Henry IV at the end of the 16th century would convert to Catholicism and said "Paris is worth a mass," Boris may say becoming prime minister is worth risking the consequences of Brexit.

Well, let’s look at it the other way then. Is there a game-changer for the ‘in’ camp? It seems as if maybe there’s a ‘silent majority’ in favour of staying in, but it’s very passive. Whereas the ‘out’ camp are such zealots, by comparison.

Yes. To quote Yeats on April 1916, the Easter Rising, "The best lack all conviction and the worst are full of passionate intensity." That I think fairly sums up the difference between pro and anti-Europeans in Britain. That said, that’s been the assumption of pollsters in Britain – a silent majority, or a sleeping majority - it’s a very good phrase – for the status quo, for staying in.

All I can say is that there’s absolutely no evidence of that in recent polls and in most recent elections.

When the issue is ‘Europe’ as it was in the 2014 European parliament elections, UKIP came top. Nigel Farage got the most votes. He also got a big increase in his councillors, which people often forget – the Tories and Labour went down, UKIP went up.

When you have opinion polls on Europe, they’re much closer than they were a year ago, when there was the whole 60-65% acceptance of staying in, now they come and go, and there’s a funny paradox – which is when you do computer polls, there’s a much bigger tendency for ‘out’, when you do phone polls, voice-to-voice, there’s a bigger tendency to stay in.

Is there another lesson there from Scotland, which is at the start of the campaign the two camps were far apart, I think about 70-30% to stay together, and by the end, it was 55-45%.

Well, that’s what worries me most of all. All the referendums so far this century on the European question - bar the Spanish referendum on the draft EU constitutional treaty of, I think, January 2004, which everyone has forgotten where there was a narrow majority to stay in, because the PP and the socialists and the press were all very pro, and broadly Spain is a very pro-European country – but in all the other ones - going into the euro, the constitutional treaty in France and the Netherlands, Lisbon, Denmark and Ireland, they all have said ‘no’ to Europe. They’ve all started, though, a month, or three months, before with a very strong opinion poll lead in favour of Europe, and they all finished against.

Final question, then. As a ‘Cassandra’ who hopes against your better judgement we’ll stay in, do you think it still can be won for the ‘in’ camp?

Oh yes. I mean nothing is written in stone in electoral politics, but I don’t see the energy of the ‘in’ camp.

The ‘outs’, the ‘leaves’, have got all the money because companies that want us to stay in Britain are all listed companies and thus cannot under British law give money to political campaigning without calling a special AGM, without getting a shareholders’ vote. They’re not going to do that. They’re not going to risk getting flooded by UKIP-ers buying one share.

But on the other hand, the hedge funds, the spread-betters, the speculators, the guys who’ve done very well in the last 25 years of deregulated casino-capitalism, and who falsely think Europe would mean greater regulation – on the contrary, the more Europe can attract the world’s money to circulate here, under any conditions, the better. We should be proud of the fact that London is Europe’s Wall Street.

I mean, I wish we were also making cars, and a few other things, but the European Union would be struck a fatal blow with the exclusion of the City of London from part of its economic matrix.

But nonetheless every morning they open the Daily Telegraph, the Daily Mail, some of them open up The Sun, perhaps, and they read anti-European diatribes. And you say, "Well, can’t some read the Guardian?" Recently, the Guardian’s printed quite a lengthy diatribe by Sir Simon Jenkins in favour of Brexit, a long denunciation of Europe by Paul Mason, who’s a popular economic figure. The new rising star of left journalism, Owen Jones, a very fluent, very able commentator, he made a big appeal for a Brexit vote in the Guardian.

So the notion that parish newspapers of the liberal/left will help keep us in Europe is far from proven.