President Thabo Mbeki was expected to announce his decision on whether the Special Investigating Unit headed by Judge Willem Heath would be part of the probe into South Africa's R43-billion arms deal in Pretoria on Friday.

The debate about the probe is hotting up in parliament before the first meeting of the standing committee on public accounts next week.

In an unusual move, the Democratic Alliance's chief whip, Douglas Gibson, on Thursday launched an attack on Frene Ginwala, the speaker of the National Assembly.

He said she had failed to protect the independence of parliament in the face of pressure from the executive.

After saying that Ginwala had "contributed enormously to establishing the style and character of our democratic parliament", Gibson expressed "considerable disappointment and dismay at the way in which the speaker has let parliament down with the arms probe".

It was quite clear that the National Assembly had accepted the report of the standing committee on public accounts and resolved unanimously on a recommendation to the president that the Special Investigating Unit, together with other agencies, should be involved in the investigation, he said.

"The unanimous resolution of parliament should weigh heavily with the president and the executive. The Speaker, as the representative of parliament, should use her considerable stature to impress upon the executive that the view of parliament should not be ignored," Gibson said.

The DA was dismayed when the speaker was reported to have questioned whether parliament passed the resolution at all and then adopted a negative attitude by stating that the decision of parliament was not constitutionally binding, Gibson said.

With acknowledgment to Andre Koopman, Sapa and Independent Online.