Home Secretary Jacqui Smith says South Africans will need a visa to enter Britain in the future. They do not require one now.
The change follows concern that terrorists are exploiting the availability of stolen or forged South African passports.
Security officials say that South Africa also has become a new base for terrorist activity.
Prosecutors have alleged that a defendant in the 2006 trans-Atlantic terror plot flew to London from South Africa to lead the final stages of the plan to blow up at least seven airliners in suicide strikes.
The Home Office says it will outline visa changes later on Monday. – Sapa-AP