Fourteen members of political parties were sworn in as members of parliament's joint standing committee on intelligence on Thursday - but the Democratic Party's nominee, a former Umkhonto we Sizwe (MK) member, failed a security screening.
DP leader Tony Leon was told by national assembly Speaker Frene Ginwala on Wednesday that MP Richard Pillay had not been cleared by the National Intelligence Agency.
Members of the African National Congress-dominated committee were sworn in at parliament by Western Cape Judge-President Edwin King. The committee has one member each from the United Democratic Movement, the African Christian Democratic Party, Inkatha Freedom Party, New National Party and the Democratic Party, with the ANC making up the rest.
Ginwala said in a statement on Thursday: "Mr Leon was provided with the information which led to the denial of such clearance to the Democratic Party nominee.
"It was agreed that he would be free to share this information with his close colleagues and the nominee."
As an MK freedom fighter, Mr Pillay was detained at the infamous Quattro camp in Angola in the late '80s, apparently on suspicion of being a South African spy.
He was held in solitary confinement for extended periods.
He returned to South Africa in the early '90s and was sent by the ANC to eastern Europe for counter-intelligence training, according to DP sources.
He later worked for trade unions, including the Unemployed Masses of South Africa which aligned itself to the DP last year.
DP chief whip Douglas Gibson said that Leon had been given assurances that Pillay's rejection by the NIA was not related to his previous political career.
Gibson said his party could appeal against the decision or recommend someone else to the intelligence committee.
He said it was ironic that the NIA vetted applicants to a committee that was to monitor NIA activities.
Committee chairman Nosiviwe Mapisa-Nqakula said at a briefing after it was sworn in that the committee had not yet received a report on Pillay's rejection.
She said members of the committee were not only "civil society's elected representatives for overseeing the work of the intelligence services, but also the custodians of the nation's secrets".
"This is a heavy responsibility and calls for absolute integrity and the ability to rise above party politicking when issues of national intelligence are discussed."
The committee would not hesitate to act decisively if any intelligence actions were found to be contrary to the constitution or the laws governing the country.
Mapisa-Nqakula said the committee's first priority would be to choose an intelligence inspector-general.
A call for nominations would begin immediately and would close on February 29.
Intelligence legislation stipulates that an inspector-general "shall be a South African citizen who is a fit and proper person to hold such office".
Nominations should be forwarded to PO Box 15, Cape Town 8000 or handed in at Room 515, Marks Building, Parliament.