Police forces are using stop-and-search tactics to seize knives from youths
Downing Street has been rebuked for manipulating knife crime statistics for political ends.
Sir Michael Scholar, head of the UK Statistics Authority, said officials pleaded with No 10 not to release "unchecked" and "selective" numbers.
But they were over-ruled by ministers eager to show a crackdown on knife crime in England was working.
The Lib Dems said ministers had been "caught peddling dodgy statistics". The Tories called for the full figures.
Mr Scholar's comments came in an official letter of complaint to the Permanent Secretary at 10 Downing Street, Jeremy Heywood.
In a letter to Sir Michael on Friday evening, Mr Heywood acknowledged that "insufficient attention" appeared to have been given to the objections of statisticians to the release of the information.
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.
The Home Office was repeatedly asked by news organisations for the raw data behind the claimed falls in knife carrying but officials declined to provide the figures, saying the full information would only be published "in due course".
Sir Michael told BBC Radio 4's PM 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
He said the decision to publish the figures was tantamount to a leak, which was "rather odd because it's made with the authority of the home secretary and with Number 10 Downing Street's authority".
The government had "breached" the code governing official statistics by publishing just "one part" of the numbers.
"There is a code designed to prevent political manipulation and my authority was set up to police this code," he told BBC News.
"I am sorry to say the Home Office and No 10 broke these rules."
Sir Michael has written to leading civil servants in No 10 and the Home Office to express his concern about the robustness of the figures and the manner in which they were released.
In his letter, he said the figures were not due for release "for some time" and that officials at the ONS - which the Authority oversees - tried to stop their release.
The figures were provisional, he said, and had not passed through the "regular process of checking and quality assurance".
Sir Michael said he had been told by Office for National Statistics (ONS) officials that "officials or advisers in No 10 caused the Home Office to issue a press release" containing the information.
"I hope you will agree that the publication of prematurely released and unchecked statistics is corrosive of public trust in official statistics and incompatible with the high standards which we are all seeking to establish," he wrote.
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.
The 'Tackling Knives Action Programme' saw increased use of stop-and-search powers and advertising campaigns warning about the dangers of carrying knives and the penalties for doing so.
The figures suggested the number of people stopped and searched each month had risen by 10,000 since June and those found carrying knives were three times more likely to be sent to prison.
At the time, Home Secretary Jacqui Smith welcomed the fact the crackdown was "making a real difference on the ground" but said more needed to be done.
The figures in question were released on the same day that Gordon Brown joined campaigners, including relatives of victims of knife crime, to launch a new drive against knife violence.
'Culture of spin'
But with question marks now raised about the data, the Tories called for ministers to explain themselves.
"The knife crime epidemic is a tragedy that has claimed too many young lives," said shadow home secretary Dominic Grieve.
"If government ministers have sanctioned the selective and manipulative spinning of these statistics, it is reckless and irresponsible."
The UK Statistics Authority was created last year as part of a move to give ONS its operational independence and to improve trust in public statistics.
"Labour should immediately publish the full figures so that we can see the truth," Mr Grieve added.
For the Lib Dems, shadow home affairs spokesman Chris Huhne said "the culture of spin" seemed to be alive and well at the heart of government.
"If ministers want the British people to trust anything they say, statistics must be made completely independent of government," he said.
"Unfortunately it still seems that ministers are prepared to put courting the headlines ahead of checking the facts."
The BBC's Mark Easton said the episode was damaging for trust in crime figures and official statistics in general.