Prime Minister Sir Keir Starmer has said he was determined to fight the “poison” of antisemitism during a visit to the site of Auschwitz.

Sir Keir, in Poland for talks with the country’s political leaders to discuss defence and security, said nothing could have prepared him for the horror of what he had seen.

“It is utterly harrowing,” the prime minister said. “The mounds of hair, the shoes, the suitcases, the names and details, everything that was so meticulously kept, except for human life,” he added.

In a news conference with Polish Prime Minister Donald Tusk, Sir Keir said he was determined to deepen the two countries’ security collaborations.

Sir Keir’s visit comes just over a week before the 80th anniversary of the liberation of Auschwitz-Birkenau, which was the largest Nazi concentration camp.

Six million Jews were murdered by the Nazis and their accomplices during World War Two.

The prime minister recalled feeling “a sickness” and “air of desolation” as he tried to make sense of “the enormity of this barbarous, planned, industrialised murder”.

The visit, Sir Keir said, showed “more clearly than ever before” that the Holocaust “took a collective endeavour by thousands of ordinary people who each played their part in constructing this whole industry of death”.

He was joined by his wife Lady Victoria Starmer, who is Jewish and had visited Auschwitz once before.

She was equally moved, the prime minister said, adding: “It was her second visit, but no less harrowing than the first time she stepped through that gate and witnessed the depravity of what happened here.”

While in Poland, Sir Keir and Tusk discussed defence, energy security, climate and illegal migration in Europe, the prime minister told a news conference.

Speaking about cooperation between the UK and the EU, Tusk said he hoped for a “Breturn”, adding: “I’d rather be an optimist and harbour these dreams in my heart – sometimes they come true in politics.”

Sir Keir went on to emphasise that Poland and the UK share an “unbreakable commitment” to both Nato and Ukraine.

Hailing a UK-Poland treaty, which is yet to be ratified, the prime minister said it would cover all aspects of threats faced by the two countries, including “deepening ties between our defence industries”.

His visit to Poland comes one day after he pledged to put Ukraine in the “strongest possible position” on a trip to Kyiv where he signed a “landmark” 100-year pact with the war-stricken country.

The prime minister condemned the lack of consistency when people use the phrase “never again”, as people rightly condemn the persecution of Jewish people during World War Two, but fail to call out antisemitism in other circumstances.

“But where is never again, when we see the poison of antisemitism rising around the world in aftermath of October 7?

“Where is never again, when the pulse of fear is beating in our own Jewish community, as people are despicably targeted once again for the very same reason, because they are Jewish,” Sir Keir added.

The Holocaust Memorial Day Trust has said that antisemitism in the UK and globally has increased significantly following 7 October attacks in Israel by Hamas and the subsequent war in Gaza.

Hamas fighters stormed across Israel’s southern border on 7 October 2023, killing about 1,200 people and taking more than 250 hostages back to Gaza. Israel retaliated with a military offensive, which has been ongoing for more than 15 months.

Last August, the Community Security Trust – a Jewish security charity – said reports of antisemitic incidents in the UK in the first half of 2024 had reached another record high. The charity said the record-high figures were a continuation of the impact of antisemitic reactions to the 7 October attack and ongoing war in Gaza.

Sir Keir’s visit comes as Israel and Hamas agreed to a ceasefire and hostage release deal in Gaza, which is due to begin on Sunday.

The agreement, more than 15 months after the start of the war in Gaza, will see 33 hostages taken from Israel by Hamas returned in the first stage of the deal, Qatari negotiators have said.