Nick Clegg suffered a resounding defeat in Wednesday's televised Europe debate with Nigel Farage, according to an instant Guardian/ICM poll. Of viewers giving a verdict, 69% said Ukip's frontman had won, with just 31% giving victory to the Liberal Democrat leader.

Viewers also judged, by 49% to 39%, that Nigel Farage came across as having the "more appealing personality". By an emphatic 64% to 30% margin viewers thought he had the better arguments.

Farage was judged the victor with ICM across all age groups and regions, and even among viewers who had been Lib Dem voters in 2010 – only 41% of those who had backed Clegg in the last election thought he came out on top, as against 59% who thought Farage did.

Whereas only 7% of viewers say they are now more likely to vote Lib Dem in next month's Euro election, 38% say the same of Ukip.

Turning to the prospect of an in/out EU referendum, only 16% say their vote would be shifted by what they saw, against 69% who say they had already made up their mind. But overall, 53% of the sample are now inclined towards voting to "leave the EU" against 39% who say they would want to stay in.

After the first of the two Europe debates, an instant YouGov poll judged Farage to have beaten Clegg by 57% to 36% last week (with 6% don't knows). The Lib Dem press office tweeted out complaints that the poll was skewed towards more elderly and middle-class voters, because the sample was not weighted to reflect demographics.

ICM's analysis seeks to assess the effect the debate would have had on Britons as a whole had they all been watching, by adjusting for age, sex and region, as well as recalled vote from the last general election. Yet Clegg's defeat with ICM this week was more emphatic than with YouGov last week. And a fresh YouGov poll mirrored ICM's findings closely – YouGov found 68% judging Farage had performed better, against 27% for Clegg, and 5% unsure.

Voters who continue to back the Lib Dems were the only group who believe that the deputy prime minister won the night – by 58% to 42%. With the Lib Dem/Labour flank regarded as one of the more competitive parts of the political field, Clegg will be particularly dismayed that 57% of existing Labour supporters gave Nigel Farage the night, as against just 43% who called the evening for Clegg.

ICM Research interviewed a random sample of 1,458 adults aged 18+ who had watched the debate on 2 April. Respondents were warned that the survey invitation was coming, and agreed to complete the questionnaire immediately after the debate finished. Interviews were conducted online, and the results have been weighted to the profile of all adults. ICM is a member of the British Polling Council and abides by its rules.