Theresa May was speaking at the Davos World Economic Forum
Speaking in Davos, Switzerland, Mrs May said: "Those of us who meet here are all optimists who believe in the power of public and private cooperation to make the world of tomorrow better than today.
"We are all united in our belief that that world will be built on the foundation of free trade, partnership and globalisation yet beyond the confines of this hall those forces for good we take for granted are being called in to question the forces of liberations, free trade that have an overwhelming impact on our world, the forces that underpin the rules based international system which is key to our global beliefs of unity are at risk of being undermined.
"Across Europe parties of the far left and right are seeking to exploit this opportunity gathering support by feeding off an underlying sense felt by some people with modest to low incomes living in relatively rich countries in the west are not working for them.
"Those parties who embrace the politics of division and despair, who offer solutions which are easy, feed off the sense in the public that mainstream and political leaders have failed to address their problems."
This was Mrs May's first time in the alpine resort speaking as Britain's Prime Minister.
A source earlier this morning said the message "won't be combative" but said: "The PM is reflecting themes she's spoken about before – that change has to come in order to benefit who have been left behind."
As Home Secretary Mrs May introduced the Modern Slavery Act to Britain two years ago.
The Davos summit has already proved eventful, with US Vice President Joe Biden yesterday accusing Russian president Vladimir Putin of using "corruption" to destroy the Western, liberal world order.
He also urged against “Islamaphobia” and “building walls”.
Mr Biden said Russia is trying to use underhand tactics to expose faultlines in the EU and slowly erode it until it crumbles.
The 74-year-old said the nationalist wave sweeping across the world, as evidenced by Brexit, Trump's election and Marine le Pen's meteoric rise in France, was a potentially "dangerous" thing.
Mr Biden said: "Some people are trying to capitalise on this anti-Islamic spirit. They think the answer is to build walls and shut the gates.
"But that's precisely the wrong answer. It doesn't resolve the causes of those problems.
"Illiberal actors will equate their success with ruining the international order."
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