AN unprecedented surge in support for the Liberal Democrats has followed Nick Clegg's "victory" in the first prime ministerial debate, an astonishing reflection of the power of the inaugural TV event.
Support for the Liberals among those who watched Thursday night's programme rocketed from 21 per cent beforehand to 35 per cent immediately afterwards, according to a poll of 4,000 viewers released yesterday.
Polling company ComRes said that the programme, watched at its peak by ten million people, had at a stroke taken the party to its highest polling rating of the year, four points behind Labour.
That surge in Lib Dem support immediately forced bookmakers to cut their odds on a hung parliament, one in which an enlarged Liberal group could hold the balance of power over either the Tories or Labour.
The remarkable shift in opinion prompted those two parties to begin a counterattack against Liberal policies with the Tories branding Lib Dem policies "eccentric". With the second TV debate next week focusing on foreign affairs, Mr Brown and Mr Cameron are expected to "double-up" on Mr Clegg's opposition to the Trident nuclear weapons programme and his backing for entry to the euro.
But while the Tories and Labour were reassessing their strategy towards the Lib Dems, the polls suggested the main losers from the debate were not the two big parties but the missing smaller parties, including the SNP. Support for "others" among those watching on Thursday collapsed from 13 per cent before the programme to just 5 per cent afterwards.
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That finding is sure to add to protests from the Scottish Nationalists over their exclusion from the debate, amid evidence that up to 600,000 Scots ignored Alex Salmond's claim that the debates would be "meaningless" and tuned in.
The debate has been interpreted as a landmark moment for the Lib Dems, so often forced on to the sidelines by the big two.
Given equal status to David Cameron and Gordon Brown, Mr Clegg was able to declare a plague on both Tory and Labour houses, winning overwhelming support from viewers at home.
ComRes said yesterday that, based on the sample of TV viewers who watched, Lib Dem support was now at 24 per cent, its highest since September last year. Labour were at 28 per cent, and the Conservatives on 35 per cent.
Former Lib Dem leader Lord Ashdown said the debate was "potentially a game-changer". Labour's election co-ordinator, Douglas Alexander, accepted that, following the debate, "anything is possible".
He added: "A sceptical public is taking a long, hard look at each of the leaders and each of the parties before making their choice. None of us can be sure as to the outcome."
Mr Clegg tried to play down expectations yesterday, with his party well aware that it faces an onslaught from its rivals in the wake of the debate.
He said: "The leaders' debate is the first step. There's still quite a long way to go until people make up their minds – there are more leaders' debates. Hopefully, it will have given people the sense that there are some real choices to be made.
"It's not just a choice between the two old parties, between the Tweedledee and Tweedledum of British politics, the Labour and Conservative parties. We offer something new and different."
Conservative leader Mr Cameron conceded that Mr Clegg had won the debate amid concerns in Tory circles that they had made a major strategic blunder in agreeing to it being held. A small swing from Conservative to Liberal would hand Mr Clegg's party several key Tory marginals, including the Dorset West constituency held by Oliver Letwin.
Mr Cameron claimed: "I always knew that if you do debates, you are going to give them (the Liberals] a massive platform but I always thought it was worthwhile."
In Scotland, the outcome of the debate will give the Liberal Democrats renewed confidence that they can cling on to seats such as East Dunbartonshire and Dunfermline and West Fife, while making gains in seats such as Edinburgh South.
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Mr Brown also appeared to concede that Mr Clegg had won the debate. "I think he'll be rightly pleased with his performance," he said.
Mr Brown claimed, however, that voters did not know as much about Lib Dem policies as they did about Labour and Tory plans.
Both those parties gave notice yesterday that the "free run" enjoyed by Mr Clegg on Thursday night could not be expected to last.
Conservative education spokesman Michael Gove said: "While Nick Clegg is a very attractive individual in many ways, the policies of his party are outside the mainstream and a little bit eccentric – not necessarily what you would want at a time of crisis and difficulty."
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On a visit to Glasgow yesterday, shadow chancellor George Osborne criticised the party's inconsistency over its plans to get rid of the Trident nuclear deterrent.
"Why is it that the national leader on TV says he is going to abolish Trident when, if you go to Argyll, the local Lib Dems are saying Faslane is really important to the local Scottish economy?"
He added: "That is one example of the scrutiny that is going to come the Lib Dems' way, and they are welcome to it."
The SNP also criticised Mr Clegg's claims on Thursday night that he would scrap Trident. Mr Clegg has said that he thinks a cheaper replacement for Trident can be found.
Labour continued to highlight where they agreed with the Liberals yesterday, offering further evidence that Mr Brown is hoping to woo Mr Clegg in the event of a hung parliament.