Support for the Conservatives at the European elections slumps to 11%, less than a third of what the Farage’s party is polling

Senior Tory and Labour politicians have issued frantic calls to their voters to back them in next week’s European elections after a new poll showed support for Nigel Farage’s Brexit party had soared to a level higher than for the two main parties put together.

The Opinium survey for the Observer places the Brexit party on 34%, when people were asked how they intended to vote on 23 May, with Labour slipping to 21% and the Conservatives collapsing to just 11%. Ominously for Theresa May, support for the Tories at the European elections is now less than a third of that for Farage’s party, and below that for the Liberal Democrats, who are on 12%.

The poll suggests the Brexit party, launched only last month, is now on course for a thumping victory that Farage will, MPs fear, use to back his argument that the UK must leave the EU immediately without a deal.

On Saturday Farage was cheered by hundreds of voters at a rally in Houghton-le-Spring, near Sunderland, as he described the prime minister’s Brexit deal as “like a surrender document of a nation that has been defeated in war”.

There were signs of mounting panic and recriminations in both Tory and Labour ranks as their MPs attempted belatedly to mount “stop Farage” operations.

May was accused by senior Conservatives of “fuelling populism” with her indecision over the Brexit issue, while Labour politicians urged their backers to come out and vote despite the party’s mixed messages on Europe, which are depressing its support.

Richard Corbett, Labour’s leader in the European parliament, said: “Labour voters must turn out and vote to stop a far-right extremist claiming he represents Britain.”

Writing for the Observer online, the former prime minister Tony Blair says it is vital that Labour supporters go to the polls, even if they choose a party more clearly in favour of Remain than Labour.

“This is not a vote to choose a prime minister or a government,” Blair says. “It is a vote for the Farage Brexit; or against it.”

He adds: “I will vote Labour because I believe ultimately Labour will be counted on the anti-Farage side of the ledger. The bulk of the Labour party membership, MPs and voters are against Brexit and certainly against that Brexit advocated by the Brexit party and its fellow travellers in the Conservative party.”

A series of Conservative moderates demanded that the party take on Farage directly, rather than give him a free run in the campaign. The former education secretary Nicky Morgan said it was time to tackle the “politics of division” head on. “It is a dangerous path for any democracy and we know where it ends – a deeply fragmented and weakened country. Those of us who can see the dangers must call this kind of politics out at every opportunity we get.”

Facebook Twitter Pinterest A campaign event for the Brexit party in Houghton-le-Spring on 11 May. Photograph: Ian Forsyth/Getty Images

Another former education secretary, Justine Greening, added: “The cabinet’s halfway-house fudged Brexit pleases no one. Failing to realise that and ducking tough decisions is just fuelling populism. In reality the EU election will not break the gridlock in parliament so it solves nothing – the only way to really resolve Brexit is a straight choice in a second referendum with Remain, the PM’s deal and WTO Brexit on the ballot. Only then will we really know what the people’s choice is.”

Sam Gyimah, the former universities minister, said: “Harnessing grievance is Farage’s only card, but we know he’s never had a solid plan for our great country. We have vacated the pitch, and voters are flocking to him. Time to call him out.”

In an attempt to show that May still believes a Brexit deal is possible, Downing Street said on Saturday night that talks between the government and Labour would resume on Monday afternoon. Then the government intends to explore with the EU when it might discuss changes to the political declaration that have been under discussion with Labour, including those relating to customs arrangements, workers’ rights and environmental protections.

Farage’s rise will, however, inevitably raise new doubts about how long May can survive as Tory leader, as pressure mounts on her from her own backbenchers to step down. Cabinet ministers say the party is haemorrhaging support, with Leavers flocking to Farage’s party and Tory Remainers either saying they will refuse to vote or back another party.

The Opinium poll also makes grim reading for the Tories and Labour when voters were asked how they would vote at a general election. Labour is on 28%, while the Tories are on 22%, just one point ahead of the Brexit party on 21%.

On Monday the acting leader of the pro-Remain party Change UK, Heidi Allen, will use a party political broadcast to challenge Farage to a television debate. Chuka Umunna, the former Labour MP who defected to the new party, said on Saturday night: “If you look beyond the razzmatazz, let’s not forget this is still the man responsible for whipping up anti-immigrant sentiment in this country with, for example, his Leave.EU ‘Breaking Point’ poster. But he is being given a free ride in these elections by a Brexit-supporting media. It’s about time this nasty, divisive politics was challenged, which is why we are calling for a leaders’ debate before polling day.”

The former Conservative foreign minister Alistair Burt said: “I would hope voters would return to the Conservative party in a general election, but we have no entitlement to them. While we must address those voting Brexit, we should not be misled that only a hard-right agenda would do so, and reject leadership candidates if they pander to that. Conservatives should work together urgently to ensure a moderate, centre-right party is seen as fit to tackle a much wider set of social, national and international issues.”

A ComRes poll for the Sunday Telegraph showed that if a Westminster general election were called, Labour would reap the largest share of the vote with 27%; the Brexit party would garner 20% ahead of the Conservatives on 19%. The Liberal Democrats would win 14%, followed by ChangeUK (7%) and the Greens (5%) with Ukip trailing on 2%.