Sir Keir Starmer will host around 45 European leaders on Thursday at a summit he hopes will begin to reset Britain’s relationship with the continent.

The gathering of the European Political Community (EPC) will give leaders a chance to reaffirm support for Ukraine and discuss key shared concerns such as migration and energy.

The summit at Blenheim Palace near Oxford will also allow the prime minister an early opportunity to meet scores of European allies only weeks into his premiership.

Ahead of the meeting, Sir Keir promised the UK would have a “more active and greater convening role on the world stage”.

He added: “The EPC will fire the starting gun on this government’s new approach to Europe, one that will not just benefit us now, but for generations to come, from dismantling the people-smuggling webs trafficking people across Europe, to standing up to Putin’s barbaric actions in Ukraine and destabilising activity across Europe.”

There will be greater European efforts to tackle people-smuggling gangs, and faster asylum decisions, with 100 Home Office staff redeployed to help return failed claimants to their country of origin.

The EPC was set up in 2022 in response to Russia’s invasion of Ukraine as a way of bringing together European heads of government – from both the EU and outside – for informal talks.

Ukrainian President Volodymyr Zelensky is expected to attend the gathering only a week after Nato leaders promised his country more air defences, but no invitation to join the military alliance.

Lord Ricketts, former national security adviser, said the summit would help “put Britain back at the centre of European diplomacy” although most discussions would be about the war in Ukraine.

“The main headline will be European leaders coming together to show united support for Ukraine and Zelensky at a time of political uncertainty in the United States,” he said.

The summit will also give the prime minister the chance to set out to EU leaders his hopes of agreeing a new security and defence pact with the bloc.

He will be accompanied by Foreign Secretary David Lammy, minister for EU relations Nick Thomas-Symonds and Europe minister Stephen Doughty.

But any EU-focused discussions will not involve the European Commission President, Ursula von der Leyen, because the hearing and vote confirming her expected reappointment takes place in Strasbourg on the same day.

Sir Keir is due to hold separate face-to-face meetings with the Taoiseach (Irish prime minister) Simon Harris, the Polish Prime Minister Donald Tusk and then French President Emmanuel Macron at a private dinner at Blenheim.

Labour’s manifesto promised to make the UK “a leading nation in Europe once again, with an improved and ambitious relationship with our European partners”.

EU officials say they would be happy to discuss closer security cooperation, but say detailed negotiations are the future. They warn EU members may demand concessions from the UK in return on issues like fishing rights and youth mobility.

Charles Grant, director of the Centre for European Reform, said the summit will allow Sir Keir to “hobnob and establish human connections” with European leaders he has never met. It will also give the PM a chance “to set out the direction and scope” of how he wants to reset UK-EU relations.

“Keir Starmer’s personality in itself will do more than people realise,” Mr Grant said.

“He is diligent, sensible, serious, he reads his briefs, he believes in the rule of law and international institutions. The Europeans will like that.”

Also invited to the EPC – for the first time – are the general secretaries of Nato, the Council of Europe and the Organization for Security and Cooperation in Europe to discuss what Downing Street calls the “arc of conflict and instability inside and near Europe’s borders”.

The formal summit agenda involves separate discussions on tackling illegal migration and people trafficking, beefing up Europe’s energy security, and defending democracy and countering disinformation.

The prime minister will attend the migration working group, co-chaired by Italy’s right wing leader, Georgia Meloni.

In informal bilateral talks on the margins of the summit, leaders are also expected to discuss how best to prepare Europe for a possible Donald Trump presidency, with the risk of a global trade war and declining US military support for Ukraine.

The prime minister said that “Europe is at the forefront of some of the greatest challenges of our time.”

“Russia’s barbaric war continues to reverberate across our continent, while vile smuggling gangs traffic innocent people on perilous journeys that too often end in tragedy,” he said.

“We cannot be spectators in this chapter of history. We must do more and go further, not just for the courageous Ukrainians on the frontlines, or those being trafficked from country-to-country, but so our future generations look back with pride at what our continent achieved together.”

He said that he promised to “change the way the UK engages with our European partners, working collaboratively to drive forward progress on these generational challenges”, adding that work begins at the summit.

This is only the fourth meeting of the EPC, the brainchild of President Macron. The previous biannual summits were held in the Czech Republic in 2022, and then Moldova and Spain last year.

The next country to host the EPC later this year is Hungary whose leader, Viktor Orban, is close to Vladimir Putin and resists Nato support for Ukraine.

There are questions about how much the diplomatic format can achieve. It has no secretariat, it takes no decisions, it agrees no communiques. Critics say it is little more than a talking shop. They also say the membership is so large that a shared agenda, let alone agreement, is hard to reach.

But supporters say the informal discussions without framework give heads of government a rare chance to talk and work through problems. They also say it is one of the few bodies that brings together EU and non-EU countries.

Blenheim Palace was chosen as a venue in part because of its symbolism as the birthplace of Winston Churchill, who in 1946 called for “a kind of United States of Europe…a structure under which it can dwell in peace, in safety and in freedom”.

However, the leaders will walk through grand corridors with paintings reminding them the Baroque mansion was named after a great battle of European powers in 1704 that saw Britain and Austria defeat French and Bavarian forces.