sentences:  In talks at Chequers, Thatcher told Botha the policy of racial separation was "unacceptable".She urged him to free jailed black leader Nelson Mandela; to halt the harassment of black dissidents; to stop the bombing of African National Congress (ANC) guerrilla bases in front-line states; and to comply with UN Security Council resolutions and withdraw from Namibia.Thatcher defended Botha's visit as an encouragement to reform, but he ignored her concern over Mandela's continued detainment, and although a new constitution brought coloured people of mixed race and Indians into a tricameral assembly, 22 million blacks continued to be excluded from the representation.