Charles, 74, had rolled out traditional pomp and ceremony to welcome Ramaphosa, hosted a banquet in his honour on Tuesday. Ramaphosa also addressed lawmakers at the Houses of Parliament.
On Wednesday, Britain announced a new set of research collaborations as Ramaphosa toured the Crick Institute, the biggest biomedical research facility in Europe, and Kew Gardens, with Charles' brother Edward.
British foreign minister James Cleverly said the partnerships, on areas such as vaccine manufacturing, genome sequencing and climate change, will "benefit us all".
"The UK and South Africa have shown global leadership in joining together to protect people by preventing the spread of dangerous diseases, and by working to halt climate change."
Ramaphosa met Prime Minister Rishi Sunak later in the day, and attended a UK-South Africa business forum to discuss trade and investment. South Africa is Britain's biggest trading partner in Africa.
Ramaphosa had highlighted the role that industrialised nations had to play in helping other countries cut emissions in his speech on Tuesday, and welcomed Britain's involvement in initiatives helping South Africa to decarbonise.
Britain will support genome sequencing at South Africa's National Institute for Communicable Diseases (NICD), which played a key role in detecting Covid-19 variants such as beta and omicron, in a push to improve antimicrobial resistance surveillance in Africa.
Kew Gardens - a botanical garden in west London - will also work with South Africa's National Biodiversity Institute on preserving South Africa's plant diversity.
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