The Heath anti-corruption unit will make a special representation to President Mbeki in a last-ditch attempt to be included in the investigation of the R43-billion arms deal.

Mbeki is expected to announce his decision on Wednesday or Thursday. He was still "considering the matter", said his spokesperson, Nazeem Mahatey, on Tuesday.

On Monday, Justice Minister Penuell Maduna said he had advised the president against issuing a proclamation to enable Heath's special investigating unit to join the multi-agency investigation. Mbeki was highly unlikely to disregard Maduna's advice, observers said.

Maduna's decision not to support the involvement of Judge Heath in the probe has been criticised by opposition parties, who say the unit's corruption-busting experience would be invaluable in a complex investigation.

The minister was also accused of disregarding the advice of parliament.

Parliament's watchdog on public finances, the standing committee on public accounts (Scopa), recommended an investigation of the arms deal after the publication of an auditor-general's report highlighting irregularities in the bid process.

The committee recommended a multi-agency probe involving the Heath unit, the auditor-general, the public protector and national director of public prosecutions, through his special directorate for serious economic offences.

Parliament subsequently adopted a motion calling on Mbeki to issue a proclamation enabling the Heath unit to join the probe.

Although Maduna maintains the motion is not binding on the president, Pan Africanist Congress MP Patricia de Lille, who moved the motion in the national assembly on November 2 last year, said she would go to court to force the government to implement it.

The Heath unit said in a statement on Tuesday that it was disappointed with Maduna's recommendation to the president that the unit not be involved in the investigation.

But it accepted that it could only investigate matters referred to it by the president, and would abide by whatever decision he made.

The unit said it would make its own representations to Mbeki in an effort to win his support.

Meanwhile, the Democratic Alliance said the reasons given by Maduna for his advice to the president were "fundamentally flawed".

Maduna's argument that the Heath unit's workload was already too high was a "smokescreen", said MP Raenette Taljaard, the DA's spokesperson on public enterprises.

"South Africa cannot afford a perception of a corruption-complicit executive to take root in the mind of prospective foreign investors when they consider us as an emerging-market, foreign direct investment destination

"No amount of spin doctoring ... will be able to undo the damage done if the arms probe smacks of a cover-up."

With acknowledgement to Robert Brand and Independent Online.