British Prime Minister Theresa May will "raise deep concerns at the humanitarian situation" in war-torn Yemen with Saudi Crown Prince Mohammed bin Salman during his visit to Britain beginning on Wednesday, according to her spokesman.

"[May] will acknowledge the steps taken recently by Saudi Arabia to address the crisis but stress the importance of full and unfettered humanitarian and commercial access, including through the ports," he said on Tuesday.

"She will also reiterate how seriously we take allegations of violation against international humanitarian law and emphasise the need to ensure these are investigated swiftly and thoroughly."

The spokesman added the prime minister would "make clear that we urgently need to see progress on the political track... to end the conflict and humanitarian suffering in Yemen".

She will also reiterate how seriously we take allegations of violation against international humanitarian law. - UK PM Theresa May's spokesman

Britain is rolling out the red carpet for the crown prince's controversial three-day visit, which Downing Street hopes "will usher in a new era in bilateral relations" but is also expected to draw protests.

Salman will lunch on Wednesday with the Queen at Buckingham Palace, while Prince Charles will host him at a dinner with Prince William among the guests.

The crown prince will jointly host with May the inaugural UK-Saudi strategic partnership council at No. 10 Downing Street, the prime minister's office and residence.

The summit, attended by ministers from both countries, will focus on support for reforms in Saudi Arabia, trade relations, defence and security, according to Downing Street.

"An important part of the visit will be exploring ways we can support Saudi to progress and intensify these reforms," May's spokesman said, noting the enacted or proposed lifting of bans on women in sports, going to cinemas and being able to drive in the kingdom.

The protest group Stop the War will hold a rally outside Downing Street on Wednesday afternoon to denounce what it said is Saudi Arabia's "brutal and illegal bombing" in Yemen and London's support for the Gulf state.

Meanwhile, the NGO Save the Children will protest the conflict by placing a life-size statue of a child near parliament "to draw attention to the violence that is being fuelled, in part, by British-made bombs".

The UK has used standard arms licences to approve more than $6.4bn in arms to Saudi Arabia since the start of the war in Yemen in 2015, including advanced jets and munitions.

But figures seen exclusively by Middle East Eye show that the government has actively overseen a more than 75 percent increase in the use of secretive "open licences" to approve additional arms sales to the kingdom, including vital parts for the jets striking targets in Yemen.

Emily Thornberry, Labour’s shadow foreign secretary, has accused May’s government of trying "to hide its role in fuelling" the war in Yemen.

She told MEE earlier this month: "Instead of seizing their responsibility to help stop this dreadful war, the government is just trying to hide its role in fuelling it."

Britain's opposition Labour Party leader Jeremy Corbyn has called on Downing Street to pressure bin Salman on the "widespread human and civil rights abuses in Saudi Arabia".

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"Theresa May should use this visit to announce the UK will no longer supply arms to Saudi Arabia while the devastating Saudi-led bombing of Yemen continues and make clear Britain's strong opposition to widespread human and civil rights abuses in Saudi Arabia," Corbyn said.

Saudi Arabia's foreign minister defended his country's "just" war in Yemen on the eve of the crown prince's visit, which follows a trip to Egypt earlier in the week and comes ahead of a visit to the United States later in March.

"They criticise us for a war in Yemen that we did not want, that was imposed on us," Adel al-Jubeir told BBC radio.

"They criticise us for a war in Yemen that is a just war, that is supported by international law," he added.

The war has killed more than 10,000 people. The UN says Yemen is the world's worst humanitarian crisis, with about eight million people on the brink of famine, a cholera epidemic and economic collapse in what was already Arabia’s poorest nation.