Nigel Farage triumphed in the second television debate on Europe by a clear-cut 69% to 31%, an instant poll showed, suggesting that a more emotional but often overscripted Nick Clegg failed to convince viewers that Ukip is selling the British people a "dangerous con" and a "fantasy".

The Guardian/ICM findings after the BBC2 debate were almost exactly matched by a separate YouGov poll for the Sun, showing that in a sometimes brutal debate, with both men accusing the other of lying, it was the Ukip leader who came out ahead by an even bigger margin than a week earlier. Farage scored points as he lashed out at big business and wealthy landowners and warned there will be violence on the streets of Europe if the EU is not dismantled and democracy handed back to nation states. He said his aim was to protect the white working class.

The result as demonstrated by the polls will be a heavy blow not just to Clegg, but also to David Cameron, who will be terrified that the two hour-long TV debates have given Ukip not just massive publicity, but political momentum for the European elections on 22 May.

The YouGov poll gave Farage 68% and Clegg 27%, a big increase on the lead he chalked up last week in the first debate, broadcast on LBC radio and Sky News, which Farage won by 57% to 36%.

Clegg will still hope to benefit from at least being the man willing to fight Ukip populism, but the image of the man that can "Stop Nigel" has been badly dented. The Lib Dem insisted afterwards he could not turn the Eurosceptic tide in the UK in two hours of debate.

But the outcome is also likely to convince Cameron that TV debates in a general election would be highly unpredictable and combustible, and therefore worth avoiding.

Throughout the debate, the two men offered competing visions of what a modern Britain can achieve in or out of Europe, with Clegg trying to portray Farage as a man who shunned the modern world, living in the 19th century.

The Ukip leader accused Clegg of wilfully lying to the British people. He called on voters to join his "people's army" to overthrow the political establishment. "Let's take back control of our country. Let's control our borders and have a proper immigration policy. Let's stop giving away £55m a day as a membership fee to a club that we don't need to be a part of. I would urge people: come and join the people's army. Let's topple the establishment who have led us to this mess."

Farage claimed immigration had led to a cut in real wages of 14% since 2007. "It's good for the rich, because it's cheaper nannies and cheaper chauffeurs and cheaper gardeners, but it's bad news for ordinary Britons." He highlighted a report by the anti-immigration group MigrationWatch that raised the prospect of 130,000 EU immigrants arriving in Britain every year.

He said: "I fear there is going to be a very big migratory wave from the Mediterranean … It [immigration] has left the white working class, effectively, as an underclass and that, I think, is a disaster."

Clegg countered by bringing out an old Ukip leaflet claiming Britons would be reduced to living on a reservation like the Native Americans if the open door to the EU continued.

Farage had been urged by his advisers to appear as an avuncular Ronald Reagan figure, but he became more apocalyptic near the end when he warned that the EU would break up in a violent way if voters across the EU were not given a vote on whether to remain members.

He said: "I want the EU to end but I want it to end democratically. If it doesn't democratically, I am afraid it will end very unpleasantly. We are already, in some countries, beginning to see the rise of worrying political extremism.

"If you take away from people their ability, through the ballot box, to change their futures because they have given away control of everything to somebody else, then I'm afraid they tend to resort to unpleasant means."

Clegg repeatedly accused Farage of wanting to turn the clock back to a simpler, bygone age in which women stayed at home. He said: "I don't believe in the dishonesty in saying to the British people that you can turn the clock back.

"What next? Are you going to say we should return to the gold standard or a pre-decimal currency, or maybe get WG Grace to open the batting for England again? This is the 21st century, it is not the 19th century."

He said Farage's politics would isolate Britain, describing it as a "sort of Billy No Mates Britain – well it will be worse than that, it will be Billy No Jobs Britain, a Billy No Influence Britain".

Before the debate, Farage had caused consternation when he suggested it was likely that the chemical weapons used in the Syrian conflict had been deployed by the Syrian opposition, and not by President Assad, a judgment that conflicts with the view of the UN and almost the entire western political establishment.

His remarks went further than Farage's own judgment last Summer when he said it was probable that Assad had deployed the weapons.

Although Clegg attacked Farage for defending Putin, describing him as the one man on the planet that is a phone call away from bringing Assad to the negotiating table , he did not directly challenge Farage to justify his claims about responsibility for the Sarin gas attack last August in Ghouta District in Damascus killing between 350 and 400 lives. He accused Farage of treating the war in Syria as a game.

Clegg said: "This isn't some sort of pub bar discussion – this is a serious issue about how we stop the slaughter, the displacement of millions of people, women and children being sexually abused, terrible violence on an unimaginable scale and all Nigel Farage can say is that he [Putin] has played it brilliantly."

But Farage mounted a full-throated attack on EU foreign policy and a called for an end to British military intervention. He told the deputy prime minister: "You were absolutely hellbent on getting involved militarily in the war in Syria, and I personally am delighted we didn't go to war in Syria, and we're not going to get involved, I hope, in military conflict in the Ukraine. The British people have had enough of endless foreign military interventions."