The national identity card is linked to people's national insurance number, the government has confirmed.
Johnson was responding to a written question from shadow home secretary Chris Grayling. More than 2,400 had applied voluntarily for a card, he said.
Johnson said the information in the UK passport database is "very similar" to that held on the National Identity Register.
In addition to NI numbers the register also held fingerprint biometrics, which will be required for passport issue "in due course", he said.
Johnson said the NI numbers help identity verification checks for identity cards, and in time, passports.
The government admitted in 2007 that it had lost nine million NI numbers, some of which were suspected of being used fraudulently.
It said at the time that the Department of Work and Pensions (DWP) had issued almost 77 million NI numbers. According to national statistics, the total UK population is 61.4 million.
Fraud and error have cost the DWP around £3bn a year for several years. In 2006, the department said it would invest in data cleansing and new IT systems to avoid errors made by officials. The National Audit Office said in October that DWP had not reported on progress with the project in 2008/2009.
A Home Office spokesman said the NI number was one of a number of checks made to verify a person's identity. "You wouldn't be able to get an ID card on the basis of the NI number alone," he said.