Up to half the passports granted under the passports-for-investment scheme may have been issued to unsuitable applicants, a former minister for justice has said.

"Perhaps as many as half of the 156 naturalisations and passports given out under this scheme have been given to unsuitable and improper people who have not fulfilled the necessary conditions," Mr Des O'Malley TD told the Dail.

Yesterday it emerged that the Department of Justice is to investigate the backgrounds of a number of people who received Irish citizenship under the passports-for-investment scheme, a move that could lead to revocation of the documents.

The decision to contact the authorities in the native countries of some of the successful passport applicants was reached by the Minister for Justice, Mr O'Donoghue, after he and officials looked at an RTE Prime Time programme in his office yesterday.

The documentary featured a native of the Czech Republic, Mr Viktor Kozeny, who received an Irish passport in 1995 but was embroiled in a financial swindle in his own country. It is understood that Mr Kozeny replied "no" to a query from the Department of Justice on his application form as to whether he had a criminal record. It appears that no further attempts were made to establish his bona fides or those of other applicants. The Irish authorities will now contact the Czech police and police in other jurisdictions to establish the records of other applicants. Mr O'Donoghue has signalled that where illegalities come to light, passports will be revoked. "I will not hesitate to take whatever action is required and available to me," the Minister said.

Raising the issue in the Dail, Mr O'Malley of the Progressive Democrats claimed that the scheme had disgraced the good name of Ireland and its public administration.

The controversial scheme, established in 1988 and scrapped last April, allowed rich non-nationals to take out Irish citizenship in return for investing in industry in this State. Just under 100 investors and 48 spouses and children were naturalised under the scheme between its inception and 1997. A spokesman for the Department of Justice said that "a handful" of passports still remained to be issued since the applications had been made prior to the suspension, and subsequent abolition, of the scheme.