United Democratic Movement leader Bantu Holomisa has launched a scathing attack on Frene Ginwala, the speaker of the national assembly, saying she and the executive were monitoring and directing the investigation into the controversial arms deal while sidelining parliament's public accounts committee.

In an open letter to Ginwala on Sunday, Holomisa said the speaker's public pronouncements on the arms-deal probe "both inside and outside Parliament leave much to be desired and have cast more shadow on the credibility of the investigation".

"It can be inferred that you and the executive are monitoring and directing the investigation" by the auditor-general, public protector and national directorate of public prosecutions, while parliament's standing committee on public accounts (Scopa) was being "systematically sidelined".

Scopa chair Gavin Woods last week also charged that his committee was being sidelined in the investigation.

Woods also claimed Ginwala had "by design" been instrumental in sidelining the committee.

Ginwala, in a sharply worded letter to Woods, made public on Sunday, called on him to apologise for remarks he had made in the press last week.

Failing this, the letter says, the committee should table an official report on Woods's claim that she influenced moves to keep the committee in the dark on the investigation.

With acknowledgment to the Parliamentary Bureau, Sapa and Independent Online.