The statement by Douglas Hurd, the Foreign Secretary, was London's most forceful criticism of Pretoria since President F W de Klerk began his reform programme in earnest two years ago.
British sources said John Major was expected to follow up the statement with a personal message to Mr de Klerk. They added that South Africa would now be high on the agenda of a summit this weekend of European Community foreign ministers, to be chaired by Britain, which holds the EC presidency.
Mr Hurd said in his statement: 'These terrible massacres threaten the prospects for peaceful change in South Africa. We look to the South African government to exert control over the security forces in Ciskei and other homelands . . . The British government calls for decisive leadership now from all the parties. There is a danger that time will run out for South Africa.'
The massacre took place only four days after an EC troika led by Mr Hurd ended a visit to South Africa, having failed to jump-start constitutional negotiations between all parties there.
A British official said yesterday that 'we don't wear the line' that Ciskei is a separate state outside Pretoria's control. He added that it appeared the ANC had strayed from the route agreed prior to the Ciskei march, and stressed that demonstrations should be conducted responsibly.
But, another official said, 'it would be entirely wrong for the South African government to use mass action as a reason to delay negotiations'.