Data protection minister Michael Wills has said he was not told that two discs containing 25 million people's data had been lost before an official statement.
Mr Wills had concerns about data sharing before the discs went missing
He told a Parliamentary committee that Chancellor Alistair Darling was right to focus on resolving the problem.
But he said he had had concerns before the discs went missing that data laws needed "toughening up" and a review had already been announced by Gordon Brown.
Plans for a national ID register would need looking at again, he added.
Anyone claiming child benefit has been urged to monitor their bank accounts after two discs, containing personal details including names, dates of birth, National Insurance and bank accounts, were apparently lost in the post.
Asked when he first heard about the problem - which the chancellor was informed about on 10 November - Mr Wills told the joint committee on human rights: "I'm afraid I learnt about it when I heard the statement in the House of Commons".
He added he thought that "perfectly reasonable" adding: "I would expect ... the responsible ministers first of all to discover the extent of the problem; and then to do whatever they could to put the problem right immediately."
He also denied knowing anything about other data breaches reported in the newspapers - but said he had yet to ascertain all the facts.
The Earl of Onslow asked: "So there are lots of leaks and you know nothing about it - and you're minister for data protection?"
The committee chairman, Labour MP Andrew Dismore, said it was "rather surprising" Mr Wills had not been informed earlier about the child benefit discs.
He told him: "If the private sector had done what the government has done they would have been had for breakfast. The problem is the government is not doing what it's preaching."
And he said the email exchange between staff at Revenue and Customs and the National Audit Office appeared to have "revolved around cost considerations" with no thought of data protection or the privacy of individuals concerned.
Mr Wills said he had concerns about data sharing within Whitehall before the loss of the discs.
But he said his department was responsible for data protection regulations and their enforcement - not to personally to stop any breaches of data protection "where and whenever they may occur".
He said it was about to be made more stringent - with proposals for tougher penalties for reckless misuse of data, including disclosure.
But he said the whole question of "mainstreaming" human rights throughout Whitehall - which include the right to privacy - would take "years".
He said: "Obviously we must learn the lessons, something wrong has happened here, something bad has happened here, we are reviewing it, we will learn the lessons and we will take action accordingly."
He added: We are going to obviously have to look at the national identity register in the light of all this. We are going to have to learn the lessons. Everything will have to be scrutinised and then we will assess it again."