Britain and South Korea will launch negotiations on a new free trade agreement (FTA) and sign a new diplomatic accord during a state visit by South Korean President Yoon Suk Yeol this week, Prime Minister Rishi Sunak's office said.

Yoon's visit officially starts on Tuesday with a welcome from King Charles, where he will receive a guard of honour and take part in a procession towards Buckingham Palace, marking the first state visit hosted by Britain since Charles' coronation.

Yoon, a conservative who has cited a "polycrisis" of global challenges as a reason for seeking closer ties with like-minded partners, will address lawmakers from both houses of parliament on Tuesday, before talks with Sunak the next day and the signing of the new accord.

"Through our new Downing Street Accord, we will drive investment, boost trade and build a friendship that not only supports global stability, but protects our interests and lasts the test of time," Sunak said in a statement, which added that talks on a new FTA would also start on Wednesday.

"I know a Free Trade Agreement fit for the future will only drive further investment, delivering on my promise to grow the economy and support highly skilled jobs."

Britain said South Korean businesses would invest 21 billion pounds ($26.17 billion) in British renewable energy and infrastructure projects, while the accord would see the countries agree to work closely on areas like semiconductors - which South Korea is a major producer of - and artificial intelligence.

The Downing Street Accord will also strengthen Britain and South Korea's joint ability to enforce U.N. sanctions against North Korea to prevent development of its nuclear weapons programmes, using sea patrols to prevent smuggling.

Speaking to members of the South Korean community, Yoon said South Korea and Britain were partners that shared universal values of freedom, human rights and rule of law, and form an economic community through trade, Yonhap news reported.

Under Yoon, South Korea has focused on strengthening economic, political, and military ties with the United States, a major ally, while seeking to maintain its trade with China and working to overcome historical disputes with long-time rival and fellow U.S. ally Japan.

"With the resumption of the free trade talks, we will lay the basis for supply chain management and mutual cooperation," he was quoted as telling the event in London, adding the two countries would also expand cooperation in cybersecurity and defence industry.

Britain is building its own ties in the Indo-Pacific as part of a tilt in its diplomatic strategy towards the region, and this year completed talks to join the Comprehensive and Progressive Agreement for Trans-Pacific Partnership.

The talks on a new trade deal with South Korea will aim to replace a carry-over agreement from when Britain left the European Union, which was based on replicating a deal with the EU from 2011 and reduced tariffs in a range of areas.

Britain said it hoped a new trade deal would pave the way for increased digital trade and streamline complex procedures, and have a new rules of origin chapter.

"This refreshed, modernised deal will boost our world-leading services sector, while also creating new opportunities for UK exports," said British business and trade minister Kemi Badenoch. ($1 = 0.8025 pounds) (Reporting by Alistair Smout, Kylie MacLellan and Sarah Young in London, additional reporting by Josh Smith in Seoul; Editing by Alistair Bell and Stephen Coates)