A World War One relic linked to one of the worst maritime disasters in English waters is to be given to South Africa by UK Prime Minister Theresa May.

The SS Mendi sank off the Isle of Wight in 1917 killing more than 600 black South Africans en route to the Western Front to support British troops.

The vessel was rammed by a British merchant ship in thick pre-dawn fog.

The prime minister will hand it to President Cyril Ramaphosa in Cape Town on Tuesday.