The crown prince of Saudi Arabia has arrived for a historic meeting with the Queen at Buckingham Palace amid widespread protests over the Middle Eastern country's human rights record.
Mohammed bin Salman was received by the monarch at the start of a trip that has brought Saudi Arabia's role in the bloody civil war in Yemen into sharp focus.
The issue was raised twice by Labour leader Jeremy Corbyn at Prime Minister's Questions on Wednesday lunchtime, when he urged Theresa May to push the crown prince on securing a political resolution to the crisis during her own private meeting with Prince Salman, 32.
Questioning the desert kingdom's treatment of dissidents, human rights defenders - as well as accusing the Government of "colluding in what the United Nations says is evidence of war crimes" - Mr Corbyn said: "As she makes her arms sales pitch, will she also call on the crown prince to halt the shocking abuse of human rights in Saudi Arabia?"
The Prime Minister said: "The link we have with Saudi Arabia is historic, it is an important one, and it has saved the lives of potentially hundreds of people in this country.
"I will be raising concerns about human rights when I meet him."
She said the UK was the third largest humanitarian donor to the stricken country, and added: "We're all concerned about the appalling humanitarian situation in Yemen and the affect it is having on people, particularly women and children. That's why, as a Government, we have increased our funding for Yemen."
Yemen has been embroiled in a bloody civil war since 2014 when rebels took over the capital city of Sanaa.
Saudi Arabia is the main player in a coalition supporting the Yemeni government against the Houthis in a war which has caused a humanitarian catastrophe.
A spokesman for the PM said she will "acknowledge the steps" taken recently by Saudi Arabia to address the crisis, but will "stress the importance of full and unfettered humanitarian and commercial access" through the ports of Hodeidah and Salif, which have previously been hit by coalition blockades.
"She will also reiterate how seriously we take allegations of violations against international humanitarian law and emphasise the need to ensure that these are investigated swiftly and thoroughly," the spokesman added.
"She will make clear that we urgently need to see progress on the political track, which is ultimately the only way to end the conflict and humanitarian suffering in Yemen."
The crown prince has been the driving force behind a modernisation programme, Vision 2030, in Saudi Arabia - but the reforms have been dismissed as a "mirage" by campaigners.
On Wednesday, he will have lunch with the Queen and dinner with the Prince of Wales and the Duke of Cambridge as the UK rolls out the red carpet for the controversial figure.
The inaugural meeting of a UK-Saudi strategic partnership council, which will meet annually to discuss bilateral and international issues, will be held at No 10 and attended by UK and Saudi ministers.
It is hoped the forum could lead to Saudi investment in and through the UK of up to £100 billion over the next 10 years.
The crown prince has also been granted rare access to a briefing on foreign policy issues, including Yemen, by national security officials.
On Thursday, the crown prince will head to Chequers for talks and a private dinner with the PM that will focus on foreign policy issues, including Yemen and Iran.
On Friday, he will meet Defence Secretary Gavin Williamson for talks.
The Government has faced criticism over its arms sales to the kingdom, but Downing Street insists it "operates one of the most robust arms export control regimes in the world".
Human rights campaigners are planning to stage a protest outside Downing Street at 5pm on Wednesday, while a life-size statue of a child was placed by Save the Children next to the Houses of Parliament to draw attention to the war in Yemen.
According to analysis by human rights charity Reprieve, executions have doubled under the Crown Prince.
The organisation said since his appointment in July 2017, 133 people had been executed compared with 67 in the previous eight months.
Amnesty International said reforms in Saudi Arabia were "largely a mirage", with "peaceful critics" of the government thrown in jail and women reliant on permission from men if they want to travel, be educated or get a job.
UK director Kate Allen said: "We'd like to see Theresa May finally showing some backbone in the UK's relationship with Saudi Arabia.
"Mrs May and her ministers should challenge the Saudi authorities over their atrocious human rights record, not swallow the unconvincing spin from Riyadh."
Rob Williams, chief executive at War Child UK - a charity for children affected by conflict, said: "Britain is complicit in the humanitarian crisis in Yemen through providing diplomatic support to Saudi Arabia, as well as selling our most high tech and deadly weapons to a coalition that the United Nations has verified as committing grave violations against children.
"I urge Theresa May to now stand for values that Britain can be proud of, a nation that sets an example to the world, that is principled and compassionate and prioritises children's lives over trade deals."