Police forces across England and Wales are routinely manipulating crime statistics in order to meet targets, a committee of MPs has heard.
A Met Police whistleblower claimed rape and sexual offences were being under-reported by as much as a quarter.
And a former West Midlands chief inspector described practices such as recording thefts as "lost property".
Committee chairman Bernard Jenkin said he was "shocked" by the claims of such manipulation "on such a wide scale".
Metropolitan Police constable James Patrick - who is currently awaiting disciplinary proceedings - told the Commons public administration committee his concerns had begun after he joined the force in 2009.
He had found robberies being logged as "theft snatch" in order to get them "off the books", he said.
After raising his concerns with an assistant commissioner, PC Patrick was moved into a specialist role looking at the measurement of crime levels, where he found disparities between numbers of burglary reports and those finally recorded.
"Burglary is an area where crimes are downgraded or moved into other brackets, such as criminal damage for attempted burglaries, or other types of thefts," he said.
An audit carried out by analysts inside the Met found that "as many as 300 burglaries would disappear within a couple of weeks", he told the committee.
Analysing 12 months of data, PC Patrick said he had also found that "the Met had effectively been under-recording rape and serious sexual offences by between 22% and 25%".
PC Patrick said he had learnt that, in an effort to avoid the perception of serious sex crimes going undetected, "a preference had developed to try to justify 'no crime' on the basis of mental health or similar issues of vulnerability or by saying that the victim has refused to disclose to them".
Former West Midlands chief inspector Dr Rodger Patrick - no relation of the constable - backed his account: "This is my experience as well. You can see that in the investigations that are being carried out, victims are being pressurised."
PC Patrick told the committee that massaging statistics had become "an ingrained part of policing culture".
London's target of a 20% crime reduction was set by the Mayor's Office for Policing and Crime and passed down the chain of command from the commissioner to constables on the beat, whose chances of promotion were linked to hitting the target.
Former Met Detective Chief Superintendent Peter Barron told the committee: "When targets are set by offices such as the Mayor's Office for Policing and Crime, what they think they are asking for are 20% fewer victims.
"That translates into 'record 20% fewer crimes' as far as... senior officers are concerned."
Mr Barron also said that inaccurate recording of crimes had an impact on the ground, as the statistics were used to determine the number of officers deployed in particular areas which were "grossly out of kilter with the real demand as opposed to the recorded demand".
He said: "There is a massive disconnect between the reality of what's happening on the ground and the formula used to determine the appropriate workforce for the borough."
He said: "The issues we are describing here are common knowledge at every level in every force within England and Wales."
And he added: "We now find ourselves in a situation where potentially forces will be amalgamating across England and Wales and, therefore, chief officers might think it is a good idea to shine bright at this time because they want to be one of the few surviving chief constables.
"How do they do that? They achieve their performance targets. This is fraud."
'Cuffing' and 'nodding'
Dr Patrick told the MPs about techniques including "cuffing", "nodding", "skewing" and "stitching" which he said officers used to make the figures look better.
He said "cuffing" crimes could involve officers deciding they did not believe complainants, recording multiple incidents in the same area as a single crime or recording thefts as "lost property", burglaries as "theft from property" and attempted burglaries as "criminal damage".
Senior officers might inappropriately take crimes off the books, he claimed.
"Nodding" involved collusion between offenders and police officers to improve detection rates, said Dr Patrick.
An offender might admit a number of offences in return for being charged for less serious offences which would result in a reduced sentence, he claimed.
The practice of "skewing" involved forces putting resources into those areas measured by performance indicators, he said.
"Stitching" suspects through the use of false confessions was "prevalent in the past, but less so now", he said.
Committee chairman Mr Jenkin said he was "shocked that apparently such manipulation of police statistics could possibly happen on such a wide scale and become so institutionally prevalent".
Mr Jenkin said: "I think what we have heard is basically how there is a system of incentives in the police that has become inherently corrupting and I think that is a very shocking thing to hear."
He added: "This is a really savage thing to say, that we can't trust the leadership of our constabularies to measure their own performance. This is what we pay our chief constables to do."
But Kent's police and crime commissioner, Ann Barnes, insisted the Kent force had now put things right, following a critical report into the way it recorded crime.
She said she had ordered a report from police inspectors, and Kent Police were now tackling the problem.
The Metropolitan Police said in a statement that it was "committed to ensuring crimes are accurately recorded and has put in place robust processes to ensure crimes are neither over- nor under-recorded".
"The crime recording of sexual offences, and rape in particular, has been audited eight times in the period September 2012 to August 2013, and has achieved an average compliance across all six areas of scrutiny of 95%."