Liberal Democrat leader Tim Farron has accused Theresa May of pursuing "aggressive, nationalistic" politics like those of Donald Trump, Vladimir Putin and Marine Le Pen during a keynote address to activists.
Speaking at the party's spring conference in York later, Mr Farron said the Prime Minister was part of a "new world order" that linked the three leaders on the political right, characterised by nationalism, authoritarianism and protectionism.
"The politics of Trump. Of Putin. Of Le Pen. And now the politics of Her Majesty's Government. Welcome to the new world order. This is the new normal, the new status quo," he said.
"Aggressive. Nationalistic. Anti-Nato. Anti-EU. It is the post-war internationalist consensus unravelling in real time. Winston Churchill's vision for a world that achieves peace through trade, common values and shared endeavour evaporating before our eyes."
Mr Farron urged his supporters to reclaim the British flag from nationalists who have turned it into a "symbol of division", saying they should never be ashamed of who they are.
"There are too many on the centre left who are squeamish about patriotism. I'm not. I love my country. I'm proud of my identity," he said.
"Patriotism isn't about dividing our society. It is about celebrating it. It's about our shared experience, our shared history, our shared destiny.
"There's nothing logical about it. It's emotional. And it's good."
Mr Farron, who has accused Labour of acting as the Tories' "accomplices" on Brexit, said the Lib Dems were the only "real opposition" to the Tories.
"We are the only party in British politics opposed to a hard Brexit, fighting for our membership of the single market and campaigning to give the British people the final say over what comes next," he said.