MPs on the Treasury Select Committee have warned that UK census details could be given to US security services if a US outsourcer wins a contract to do the census.
MPs have demanded that the government seeks assurances from the US government that census data will not be at risk if American IT outsourcer and defence company Lockheed Martin wins the census contract.
Under the US Patriot Act, which was brought in to tackle terrorism, US security services are allowed access to data held by US companies doing business abroad.
Lockheed's involvement in the Canadian census caused similar concerns in that country.
Lockheed Martin is competing with Germany's T-Systems to win a £450m contract to run the 2011 census.
The Treasury has said it will make sure that UK census data will remain in the UK out of reach from the US intelligence services, but the select committee remains unconvinced.
It said, "The committee remains concerned that the personal information gathered through the 2011 census could be subject to the US Patriot Act, and asks the government to take clear legal advice and advice from the US State Department and to publish it."