By Martin Plaut Africa analyst, BBC World Service

BAE Systems sold Hawk jets to South Africa

The Mail and Guardian has accused the UK firm of developing "a web of influence" in South Africa regarding an arms deal worth $4.5bn (£2.3bn).

In late 1999, South Africa signed a deal to upgrade its armed services.

BAE systems says it is co-operating with the investigation, but will not comment on the issues concerned.

The South African government said the weapons were needed by the armed forces after an international embargo during the apartheid era.

From the first the deal was questioned by arms campaigners.

But gradually the concerns moved to parliament, where some MPs alleged that bribes had been paid to secure various contracts.

Two South Africans have now been convicted of corruption and have been jailed.

A case against the former deputy president Jacob Zuma was withdrawn, but it is still being actively pursued.

BAE systems, which secured orders for Hawk trainers and Gripen fighters, has been investigated for the payments it is alleged to have made.

The SFO has confirmed that the investigation, which has been under way for over two years, is still active.

The BBC has been told that the SFO is planning a trip to South Africa to take the matters further but the Office has refused to comment on the matter.

Last month the British Prime Minister Tony Blair ordered the SFO to end its investigation of BAE payments to Saudi Arabia, saying that it was not in Britain's national interest.