Saudi Arabia’s crown prince is starting a three-day visit to the UK amid protests planned against his country’s role in the war in Yemen.
Mohammed bin Salman, 32, is seen by some as a modernising force in the Gulf State.
He is due to hold talks with Theresa May and have lunch with the Queen.
The UK hopes to capitalise on the Saudi economy’s opening-up but No 10 said the PM would also express “deep concern” at the humanitarian situation in Yemen.
Demonstrators are expected to protest outside Downing Street against the killing of Yemeni civilians in air strikes by a Saudi-led multinational coalition – backed by the UK and US – that is battling the rebel Houthi movement
The crown prince, who is regarded as being heir presumptive to the 82-year old King Salman, is making his first visit to the UK since taking up the role last year.
He will also have dinner with the Prince of Wales and the Duke of Cambridge.
He is credited with kick-starting economic and social reforms in the conservative desert kingdom, such as the upcoming lifting of the ban on women driving.
He also launched an anti-corruption drive that saw princes, ministers and influential businessmen detained and generated an estimated $106bn (£76bn) in settlements.
However, many have criticised his decisions to intervene in Yemen and impose a de facto blockade of neighbouring Qatar, as well as crack down on perceived opponents of his policies.
A new Strategic Partnership Council will be established which it is hoped could lead to Saudi investment in and through the UK of up to £100bn during the next 10 years.
When this relative novice on the world stage arrives in London on his first global tour since taking office, he will be granted the reddest of red carpets.
The Crown Prince is looking for international support for his internal economic reforms while at the same time trying to offer reassurance to nervous international investors.
And the British government is keen to transform a security and defence relationship into one that includes broader economic ties as well. The UK also has an unashamed appetite for inward investment from Saudi Arabia.
In other words, post-Brexit Britain will need allies, markets and money – and the Saudis are high on the UK’s wish list.
The conflict in Yemen is seen as part of a regional power struggle between Saudi Arabia, which backs the government, and Iran, which supports the Houthis but denies allegations that it is sending them weapons.
According to the United Nations, more than 9,000 people, over half of them civilians, have been killed and more than 52,000 injured in fighting in Yemen since March 2015.
Downing Street said Mrs May would “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 rebel-held ports under partial blockade by the coalition.
The PM will also call for urgent progress on securing a political resolution to the crisis, her spokesman said.
But Emily Thornberry, the foreign affairs spokeswoman for Labour, the UK’s main opposition party, urged Mrs May to use the UK’s influence to call on Saudi Arabia “to stop” the bombing in Yemen.
“We’re in a unique position to be able to intervene in this and to stop the war in Yemen and to do that as a friend,” she told BBC Radio 4’s Today programme.