Britain's grand welcome for Saudi Crown Prince Mohammed bin Salman will begin on Wednesday with a lunch with Queen Elizabeth, as the two countries seek to widen longstanding defence ties into a far-reaching partnership, Reuters reports.
Both sense an opportunity to broaden their existing relationship: Britain is looking for trading partners as it exits the European Union, and Saudi Arabia needs to convince sceptical investors about its domestic reforms.
But as Prince Mohammed and Prime Minister Theresa May meet, demonstrators will protest both countries' roles in Yemen where war has killed an estimated 10,000 people and where 8.3 million people depend on food aid and 400,000 children have life-threatening levels of malnutrition.
Inside May's Downing Street offices the two leaders will launch a "UK-Saudi Strategic Partnership Council" – an initiative to encourage Saudi Arabia's economic reforms and foster more cooperation on issues such as education and culture, as well as defence and security.
"It will usher in a new era of bilateral relations, focused on a partnership that delivers wide-ranging benefits for both of us," May's spokesman told reporters.
Britain is vying to land the stock market listing of state oil firm Saudi Aramco, but no decision is expected this week.
Later this month Prince Mohammed visits the United States, which also wants the lucrative listing, although sources said both countries may miss out.
British officials were privately delighted at the decision by Prince Mohammed, 32, to choose Britain as the major western destination on his first foreign trip since becoming heir to the Saudi throne last year.
The British government is keen to transform its historic defence relationship into two-way trade and investment, eyeing both an expanded market in Saudi Arabia for service sector exports, and attracting Saudi cash to finance domestic projects.
Business deals are possible with British defence group BAE Systems and European weapons maker MBDA, and initial agreements could be concluded on gas exploration, petrochemicals and other industries, according to British and Saudi sources.
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The three-day visit will include two audiences with the British Royal family, a briefing with national security officials, and a prestigious visit to the prime minister's country residence.
May intends to use the private dinner at Chequers, a 16th-century manor house 40 miles (60 km) northwest of London, to bring up concerns over the humanitarian crisis in Yemen, her spokesman said.
A Saudi-led military coalition is fighting the Houthi movement in Yemen, generating what the United Nation said in January was the world's worst humanitarian crisis.
"You can expect them to discuss Yemen, and the prime minister to raise deep concerns at the humanitarian situation," May's spokesman said. "She will also reiterate how seriously we take allegations of violations against international humanitarian law."
Speaking to reporters in London on Monday, Saudi foreign minister Adel al-Jubeir said his country had failed to effectively communicate the reasons behind its involvement in Yemen, but that they had not chosen to start the war.
Protestors are planning to target the Saudi officials over Yemen and other human rights issues, and Britain for licensing 4.6 billion pounds of weapons sales to Saudi Arabia since 2015.
Buses have spent two days touring London with banners accusing Prince Mohammed of war crimes, with more planned for Wednesday ahead of the main rally.
"It is vital that people show up to the protest tomorrow outside Downing Street to make clear that the UK government's complicity in the war on Yemen is not supported by the public and that we demand a peaceful and humane foreign policy," said Lindsey German of the Stop the War Coalition.