Outside Downing Street protesters organised by the Campaign Against Arms Trade are expected to gather.
Crown Prince Mohammed said the dispute with Qatar could be long-lasting, comparing it to the US embargo of Cuba imposed 60 years ago, but played down its impact, dismissing the Gulf emirate as "smaller than a Cairo street".
UK Foreign Secretary Boris Johnson also greeted the Crown Prince at the bottom of his plane when he landed on Tuesday night.
Saudi Arabia is striving to achieve real female empowerment, especially in the workplace, going beyond recent changes that allowed women to drive cars for the first time, said the country's energy minister. Later Wednesday Prince Mohammed was due to be hosted for dinner by heir-to-the-throne Prince Charles, with Prince William among the guests.
Critics remain unimpressed. Hundreds protested his United Kingdom visit outside the prime minister's residence at 10 Downing Street.
Despite all these controversies, as Britain had left European Union, the country wants to strengthen economic relations with Saudi Arabia.
"The link that 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", May said in parliament ahead of their meeting.More news: Samsung aims to inspire the 2018 Paralympic Winter Games
The United Kingdom is rolling out the red carpet for Saudi Arabia's Crown Prince, Mohammed Bin Salman (known colloquially as MBS), as he begins his first global tour.
Labour Party leader Jeremy Corbyn said during a fiery debate with May that British military advisers based in Saudia Arabia were "directing the war" in Yemen and that the United Kingdom government was colluding in what could be war crimes.
In Cairo, the crown prince asserted that his policies were working.
Britain and Saudi Arabia set out an ambition to build 65 billion pounds ($90.29 billion) of trade and investment ties in coming years, London said on Wednesday, calling the agreement a vote of confidence in the British economy ahead of Brexit.
"They should be demonstrating against the Houthis", Al Jubeir added referring to the Yemeni resistance movement that has been fighting against Saudi Arabia.
The British government's special envoy to the Saudi 2030 initiative is Ken Costa, a former churchwarden of Holy Trinity, Brompton, in London, and a former chairman of Alpha International. How does he see the visit? London also eyes listing state oil firm Saudi Aramco in its stock market.
Successive British governments have often claimed that various Saudi monarchs are reformers, yet today in Saudi Arabia you can not join a political party, you can not join a trade union, there is no freedom of assembly, and political prisoners are subject to torture, whipping and also execution.
May's Conservative government said Mohammed's visit would strengthen co-operation in "tackling global challenges such as terrorism, extremism, the conflict and humanitarian crisis in Yemen and other regional issues".