But campaigners are outraged that Britain is selling arms to Saudi Arabia while it is waging a brutal war in Yemen.
Britain and Saudi Arabia have taken a step closer to a multi-billion pound arms deal, touching on the most inflammatory element of their relationship at the end of an official visit to London which has mixed warm diplomacy with angry street protest.
Saudi Crown Prince Mohammed bin Salman has been on a three day mission to build broader trade and investment ties, meeting Queen Elizabeth, Prime Minister Theresa May and executives.
The two countries agreed to finalise talks on a multi-billion pound order for 48 Typhoon aircraft, the fighter plane's maker BAE Systems said. The deal has been under discussion for years but has proven tough to seal.
Britain and Saudi Arabia have set themselves a 65 billion pound trade and investment target for the coming years, with London looking for new post-Brexit markets for its services sector, and Prince Mohammed seeking to convince wary investors his country is a tolerant and modernising place.
But, for now the heart of bilateral trade ties remains defence and security. Britain credits Saudi intelligence sharing with saving British lives and has licensed billions of pounds of weapons and ammunition sales to Saudi Arabia.
That has provided a controversial backdrop to the warm diplomatic welcome for Prince Mohammed, with hundreds turning out on Wednesday to protest arms sales and Saudi Arabia's role in the Yemen war.
Prime Minister Theresa May defended the two countries' defence ties on Wednesday, saying all arms sales were strictly regulated, but has also repeatedly raised concerns about the humanitarian crisis in Yemen directly with Prince Mohammed.
The deal for the Typhoon fighters has become bogged down in negotiations over where production of the jet will take place, with Saudi Arabia keen to have some parts of the process on Saudi soil.
"If agreed, this shameful deal will be celebrated in the palaces of Riyadh and by the arms companies who will profit from it, but it will mean even greater destruction for the people of Yemen," said Andrew Smith of the Campaign Against Arms Trade.
The thorny topic of Yemen was on the agenda at a private dinner inside May's country residence on Thursday night, but was tempered with gifts: May's office said she presented Prince Mohammed with a family tree showing the descent of the Al Saud