Police forces are using stop-and-search tactics to seize knives from youths
The Tories have demanded an apology after Downing Street admitted releasing data on knife crime in the face of objections from statisticians.
Sir Michael Scholar, head of the UK Statistics Authority, said officials pleaded with No 10 not to release "unchecked" and "selective" numbers.
The government admitted "insufficient attention" was given to the authority's views on releasing the data.
MPs are to carry out an inquiry into the release of the data.
The government's decision has also been criticised by senior Labour backbenchers.
The authority's protests were over-ruled by ministers eager to show a crackdown on knife crime in England was working.
Responding to Sir Michael's letter of complaint, Permanent Secretary at 10 Downing Street, Jeremy Heywood said "the prime minister and all his ministers, officials and advisers take very seriously the importance of maintaining the integrity of official statistics".
But he added: "In this case...insufficient attention appears to have been given to the views of the NHS Information Centre statisticians on whether one specific data set included in the Tackling Knives Action Programme fact sheet was ready for publication."
In a press release issued on Thursday, Number 10 and the Home Office said there had been a sharp fall in the number of teenagers caught carrying knives in England and hospital admissions due to knife wounds in areas targeted by police.
They pointed to a 17% fall in serious injuries and deaths across nine police force areas over the past six months as well as a 27% fall in hospital admissions.
Sir Michael told the BBC that government statisticians had asked Number 10 not to publish the data until March when the knife crime campaign would have ended and it could be properly checked and published in its proper context.
Asked why Downing Street had acted against the advice of officials, he said: "The government was making a series of announcements about this issue and felt its case would be put better if it could publish these numbers."
I hope you will agree that the publication of prematurely released and unchecked statistics is corrosive of public trust in official statistics
Sir Michael Scholar, UK Statistics Authority
The government had "breached" the code governing official statistics by publishing just "one part" of the numbers.
Tony Wright, the Labour chairman of the Commons Public Administration Committee, said his committee will carry out the inquiry.
He told the BBC's Today programme: "We are going to find out exactly what happened in this case and make sure that an edict goes out across Whitehall that it never happens again.
"We need to find out who in Number 10 and who in the Home Office thought they could do this."
He added: "There is a new regime for the release of official statistics and this breaks the rules and it shouldn't have done."
Conservative leader David Cameron said an apology was needed from Gordon Brown.
He told Sky News: "We are not going to get anywhere with a government giving us dodgy statistics and deliberately disobeying what its own Statistics Authority is saying.
"It really is an appalling way to behave. The prime minister has got to own up to it, he's got to apologise for it and he's got to make sure it never happens again."
Immigration Minister Phil Woolas said the government had to accept the criticism but denied the figures had been manipulated.
"The idea that there is a conspiracy behind this, I goodness wish that Whitehall was so sophisticated, I can assure you it's not.
"But the fact of the matter is that crime by knives has fallen, an that surely is what is important."
However Keith Vaz, Labour MP and chairman of the Commons Home Affairs Committee, said the early release of figures "greatly undermined" public trust in the government.
He said: "It is important that we have accurate statistics that we can rely upon in order to craft policy to resolve problems as well to gauge when legislation is working. Public trust is greatly undermined by actions such as this."
The BBC's Mark Easton said the episode was damaging for trust in crime figures and official statistics in general.
The figures covered the period since the Home Office launched a £2m campaign in June to crack down on knife carrying in 10 "hotspots" including London, Greater Manchester and the West Midlands.