US authorities will not be able to see data covering all UK households even if a US defence giant wins the contract to run the 2011 census, a minister says.
Could the next UK census be the final one of its kind?
The US Patriot Act allows personal data held by companies in the US to be made available to intelligence agencies.
But Treasury Minister Angela Eagle told MPs the government had received legal assurances this would not happen if Lockheed Martin wins the census bid.
The defence company is one of two firms competing for the £450m contract.
The other bidder is German telecoms company T-Systems, part of the Deutsche Telecom group.
MPs on the Commons Treasury sub-committee raised concerns about data security, following recent data lost by HM Revenue and Customs and the DVLA, which used a US sub-contractor to process learner driver forms.
They also quizzed Ms Eagle - the minister in charge of national statistics - about the Patriot Act, which they said could be used by the US authorities to access personal data without the consent of those concerned.
"We have received legal advice that there is no risk that that would happen," she told the committee on Wednesday.
"Some of the arrangements that would be made would ensure that data was owned and kept within the UK.
"There has been no evidence of the US Patriot Act being used to subpoena companies that are not US-based."
The 2001 Patriot Act increased the powers of US law enforcement agencies to monitor telephone and e-mail communications to combat the terror threat - but it has been criticised for infringing civil liberties.
Ms Eagle said UK-based firms would carry out the census contract on behalf of Lockheed Martin and she was "pretty confident" there would be robust safeguards on the security of data.
The company's chances of landing the contract would be affected if there were concerns about confidentiality, she told the MPs.
Asked whether there would be a clause in the contract forbidding personal information being sent out of the UK at all, she said she would write to the committee in confidence.
But she added that the census had a 200-year record of keeping people's details secure "and we are extremely anxious, from ministers down, that this would not take place".
Lockheed Martin was involved in running the 2001 census in the UK, when it won a £54m contract to check postcodes and process returned forms.
The government estimated it saved £15m by using a private contractor but the firm was criticised for the late delivery of work. The budget for the 2001 census was £207m.
A full census of the UK population takes place every 10 years, with every household legally obliged to give details of who is living in their house on the day of the survey.
The 2011 census could be the last survey of its kind.
There are concerns it is no longer up to the job of providing reliable data on which to base important public spending decisions, given the UK's rapidly shifting population.
The Office of National Statistics is looking at other methods of counting the population, such as a compulsory register of addresses.
Ms Eagle told the committee she was "agnostic" about whether the 2011 survey would be the final UK census.
She said moves to replace the census with a national address register were dropped in 2006 after a row with the Ordnance Survey over intellectual property rights.
It was thought the government's ID card scheme "would provide us with a national register in due course" but it was "far too early" to say whether that would happen in practice.
Ms Eagle said a move to an address register of the type used in some other European countries, in which householders have to inform the authorities every time they change address, could be controversial.
"People in the UK are suspicious of anyone that tries to make lists.
"The issue of ID cards hasn't exactly been non-controversial - and it wouldn't be non-controversial to people to have a national address register, I'll be bound."
Earlier in the session, she said she was confident the ONS would be given an extra £25m to add a "fourth page" to the census form, which might include questions on how long people have been in the UK.
There would also be extra cash to improve the quality of population statistics generally, she told MPs.
According to figures quoted by Conservative MP Graham Brady - prepared for him by the House of Commons library from existing research - the public purse will be £9.5bn short in 2011/12 because of population underestimates.
Ms Eagle said she had not seen the figures but added: "I am confident we have got systems in place to respond if there was to be a gap of that sort."
Campaigners, led by The Green Party, have called on the government to reject Lockheed Martin's census bid over its role in the wars in Iraq and Afghanistan.