Labour leader Jeremy Corbyn is now more popular than Theresa May with the left-winger enjoying a post-general election boost, a YouGov poll released on Friday 23 June showed.
The survey, of more than 1,600 people between 21 and 22 June, found that Corbyn was respondents' prefered prime minister (35% versus 34%) as his personal rating jumped by three points, while May's fell by nine.
The research is the latest blow to the PM, who called a snap election to boost her pro-Brexit mandate.
But with the Conservatives stripped of a majority in the House of Commons after the 8 June vote, May is clinging onto power in Number 10 and is attempting to form a controversial "confidence and supply" alliance with the Democratic Unionist Party (DUP).
May's response to the Grenfell Tower fire in west London, which left at least 79 dead, was also met with criticism as the PM originally visited the scene and failed to meet with residents and victims, unlike Corbyn.
Senior Conservatives, including Foreign Secretary Boris Johnson and Environment Secretary Michael Gove, have pulled around May and put on a show of unity.
The Tories want to avoid another messy leadership contest and general election, which could see Corbyn deliver a victory for Labour and enter Number 10. The turmoil at the top of British politics comes as the gruelling two-year-long divorce talks between the UK and Brussels begin.
May is hoping to secure a bespoke customs deal with the EU so that the UK can broker its own trade deal, stop free movement of EU nationals to the UK and no longer maintain Britain's full access to the EU's single market.
Nick Clegg, the former deputy PM who lost his seat at the general election, has claimed that "Global Britain" – the government's pro-Brexit slogan – is "imperialist nostalgia".
"This seductive idea – that we can recapture the imperial reach of the past by throwing off the shackles of multilateralism – is a dangerous illusion," the ex-Liberal Democrat leader said.
"They, and other critics of the European Union, like to claim that the EU is part of the past. Instead they talk up a future in which a 'global Britain', unencumbered by EU membership, is the future.
"In truth, it's exactly the other way round: "global Britain" is in fact a euphemism for imperial nostalgia; while pooling sovereignty in our own hemisphere is the only way to influence those aspects of the modern world, from terrorism to trade, from climate change to fisheries, which cross borders."
The latest opinion poll from Survation, of more than 1,000 people on 16 and 17 June, gave Labour a three point lead over the Tories (44% versus 41%).