South Africans will be required to obtain visas to visit Britain under Government plans to close a route exploited by people smugglers, illegal immigrants and terror suspects.

The move, which will affect almost 420,000 South African nationals who enter Britain every year, is to be announced by the Home Office this week.

Whitehall sources said the changes could be put before the House of Commons today, when Jacqui Smith, the Home Secretary, and her ministerial team are scheduled to answer MPs' questions. It is likely to be controversial because South Africans form the fifth largest group of visitors to Britain after Americans, Australians, Canadians and Japanese.

The decision to require visas represents a victory for the Home Secretary in a Whitehall battle between the Home Office and the Foreign and Commonwealth Office, which opposed the idea.

The Home Secretary has decided to impose the visa regime months after warning the South African Government that it must act to make it harder for non-South African nationals to obtain a South African passport and then travel to Britain without undergoing further checks.

The Home Office threatened to impose the visa regime last July amid fears that South Africa was being used as a transit point by al-Qaeda operatives to gain entry to Britain. The South African government was given six months to introduce a range of improvements, including in the ways that passports are produced, issued and stored.

In December the Home Secretary warned the Cabinet that the cholera outbreak in neighbouring Zimbabwe might cause a huge increase in the number of Zimbabweans attempting to enter Britain, even though they too need a visa.

Law enforcement agencies have been pressing the Home Office for some time to overhaul immigration rules for South Africa amid fears that they were being exploited by people smugglers and terrorists.

The Serious Organised Crime Agency in Britain smashed a ring of people smugglers that brought more than 6,000 illegal immigrants into Britain on forged or stolen South African passports. Operation Coptine, a five-year investigation into people smuggling, resulted in the conviction of more than 40 people.

They were members of a gang operating from Leicester which, over a decade, smuggled people out of villages in India to South Africa, where they were supplied with false or stolen passports.

The migrants, who paid the gang between £5,000 and £8,000 each, were then brought to Britain, where many found work or registered as students. About a quarter of the illegal immigrants acquired British passports under different identities for travel to the United States and Canada.

Intelligence experts are also concerned that al-Qaeda has been using South Africa as a support base for fundraising and training for operations elsewhere.

Almost 420,000 South Africans entered Britain in 2007. They included 168,000 tourists, 46,200 on business, 52,800 in transit, 132,000 returning after absence abroad, 2,890 with work permits plus their 1,190 dependants. A total of 1,190 were refused entry.

Phil Woolas, Immigration Minister, said: “The Government said it would get tough and we meant it. Already our shake-up of border security is delivering results, with three million fingerprints taken from visa applicants and 3,000 people caught trying to hide their identity.”

Brazil was also warned that it faced a visa regime, but has managed to convince the Home Office that it has improved security surrounding the production and issuing of passports.

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