By Sarah Spiller
BBC File On 4
The government's ID card system will give thousands of "false matches" when more than six million people are registered on its database, an academic has claimed.
Iris scanning is thought to be the most accurate biometric
Biometric data holding a person's unique physiological characteristics will be stored on a microchip in the cards.
But Professor John Daugman, said using fingerprints as a key biometric measure will cause major problems.
The Identity and Passport Service has denied Professor Daugman's claims.
Professor Daugman, of the University of Cambridge, Computer Laboratory, said using a biometric scan of the iris - the coloured part of the eye controlling the amount of light that gets through to the retina - would give better accuracy than a fingerprint.
Plans to include the iris scan in the ID card biometric were put on hold by the government last December.
A small scale system using iris identification is operated by immigration officials at Heathrow and other UK airports.
Professor Daugman, who devised a mathematical process which converts the measurement of an iris into a record of identity, told BBC Radio 4's File On 4, he expected problems once the government's database passed the six million mark:
"Typically if you have a database of say six million people, the false match rate against them will be about one in a 1,000, and the true match rate is something like 95%.
"So this means that by the time the UK system had enrolled say six million people, which means two or three years into the roll-out, about one new person in a 1,000 will be making false matches against the database."
He added that when the next million people were added to the database there would be 1,000 false matches.
Professor Daugman, who received an OBE for his work in 1999, said the bigger the database, the bigger the problem:
"For the scheme as a whole it means that it can no longer deliver the goal of one citizen, one identity, because it cannot survive so many comparisons without making false matches - so there will be false claims of multiple identities.
"It could still be useful for other purposes but I think it would have failed for reasons that are probably to date, predictable."
He added: "I don't want to be very pessimistic and say this whole system is doomed to fail but I will say that just from analysing the mathematical requirements, if it is just fingerprint, it is unlikely to be able to succeed."
But James Hall, the chief executive of The Identity and Passport Service told File On 4: "We've always recognised that there will be question marks thrown up during the matching process and that will need to get resolved by manual intervention.
"We will work very closely with a biometric advisory group drawn from a number of experts from around the world who are giving very supportive advice around this."
Mr Hall said: "We haven't identified a date at which we will implement iris scanning. Our view is that either fingerprint or iris's would work very effectively.
He added that fingerprints had been the basis of schemes started across Europe for travellers to the USA.
For more information about this story listen to File On 4, BBC Radio 4, Tuesday 31 July 2000 BST, repeated Sunday 5 August 1700 BST.