David Cameron was urged today to ditch plans to "prevent" police from holding the DNA of rape suspects who are arrested but not charged.
Labour leader Ed Miliband said that under the Protection of Freedoms Bill, the DNA of suspected sexual offenders who were not charged would be "disposed of straight away".
But the PM insisted that the police would be "allowed to apply to keep DNA on the computer".
At Commons question time, Mr Miliband said: "You have been forced to abandon your original plans on sentencing. Will you now change your mind on the proposal to prevent police holding the DNA of those arrested but not charged with rape?"
Mr Cameron replied: "We will look carefully at the issues of DNA. But I have to say we inherited an unacceptable situation with a DNA database that had grown out of control and without proper rights to people.
"We put in place a better system, there's always room to see if it can be further improved but I think we made a big step forward from the mess we were left from the last government."
Mr Miliband said it was "a bit late" to look at the proposal as the Bill was at report stage in the Commons.
He said Rape Crisis had warned that DNA evidence was "vital" in catching rapists.
"Around 5,000 people each year are arrested on suspicion of rape and not charged," he told the PM.
"In certain cases, these individuals have gone on to commit further offences and been convicted as a result of the DNA held on the national database.
"But your proposal is that for those arrested and not charged, the DNA will be disposed of straight away. I ask you again - why is it right to discard the DNA of those arrested but not charged with rape?
"Isn't this another policy on crime that is careless, not thought through and out of touch? Why don't you think again?"
But Mr Cameron replied: "If you actually understood the policy, you would know that the police are allowed to apply to keep DNA on the computer - not something you mentioned.
"What we tend to find with your questions is that you come up with some idea, get it completely wrong in the House of Commons and we all find afterwards you've given us a partial picture."
Isabella Sankey, director of policy for Liberty, said: "Today's debate in the House shows just how much myth and misunderstanding there is about the DNA database.
"Contrary to Opposition claims, under the Government's proposals those suspected of serious offences will have their DNA automatically retained for three years.
"Of course DNA evidence is helpful in crime detection but retaining millions of innocent records is dangerous, unnecessary and expensive.
"A better way of delivering justice for victims would be to increase investment into profiling historic crime scene data and then cross-referencing against the database."