On the last day of a visit by the Saudi crown prince, Britain approved the sale of 48 highly advanced fighter jets to Saudi Arabia on Friday, brushing aside calls for an embargo over the kingdom's role in Yemen's civil war.
Sky News Defence Correspondent Alistair Bunkall said the deal is expected to be announced by Defence Secretary Gavin Williamson and the Crown Prince later this afternoon.
The jets are munufactured by British company BAe systems.
"If May really cares for the rights of people being repressed in Saudi Arabia, or bombed in Yemen, then she must stop arming and supporting the brutal Saudi dictatorship".
Mrs May defended the UK's ties with Saudi Arabia earlier this week, saying all arms sales are strictly regulated.
"Commenting on Friday's provisional deal announcement, the group said that this was a "positive step towards agreeing a contract for our valued partner".
But, in Riyadh, images of the 32-year old Saudi meeting the Christian cross-wearing head of the Anglican church on Thursday dominated newspapers, with headlines citing it as an example of the conservative kingdom's more tolerant approach to religion.
The Saudi delegation will meet May and senior ministers inside May's Downing Street offices to launch a UK-Saudi "Strategic Partnership Council" - an initiative to encourage Saudi Arabia's economic reforms and foster cooperation on issues such as education and culture, as well as defence and security. It pits Saudi Arabia's Sunni Muslim monarchy against Yemen's Houthi rebel movement, which is backed by Shiite Muslim power Iran.
Later this month Prince Mohammed visits the United States, which also wants the lucrative listing, although sources said both countries may miss out.
"The Prime Minister and Crown Prince agreed on the importance of full and unfettered humanitarian and commercial access, including through the ports, and that a political solution was ultimately the only way to end the conflict and humanitarian suffering in Yemen".