Victims are being let down, criminal cases shelved and suspects left untracked as police fail to carry out basic functions, a damning report reveals.
The findings prompted an official watchdog to raise the alarm over the "potentially perilous" state of British policing.
HM Inspectorate of Constabulary (HMIC) also issued an unprecedented warning that a shortage of detectives and investigators amounted to a "national crisis".
And it was revealed suspected murderers and rapists were among thousands wanted by forces around the country.
Inspectors said the public was being left at unacceptable risk as a minority of services artificially suppressed demand.
They uncovered evidence of emergency calls being downgraded in order to justify a slower response and failings in responding to vulnerable victims.
Fewer arrests were made, a large number of crimes were effectively "written off", suspects were not always pursued and inexperienced officers were left to carry out complex investigations, the review found.
HM Inspector Zoe Billingham stopped short of saying the service was in crisis, but warned: "We are leading to a very serious conclusion regarding the potentially perilous state of British policing in this report.
"Over the last few years, HMIC has said consistently that police forces were managing well in increasingly difficult circumstances.
"Nonetheless, today, I'm raising a red flag to warn forces of the consequences of what is, to all intents and purposes, an unconscious form of rationing of police services."
Brian Paddick, Liberal Democrat home affairs spokesman and a former senior police officer, described the findings as "totally unacceptable", adding: "How long will it be before someone dies because there is no police officer to respond?"
The wide-ranging report found:
:: Initial risk assessments made by call handlers being downgraded because of a lack of available officers to respond immediately
:: A lack of focus directed to apprehending wanted individuals, with the details of 67,000 suspects not placed on the police national computer (PNC)
:: As of August there were 45,960 wanted suspects on the database, including those being sought for offences including terrorism, murder and rape
:: In too many cases "insufficient action" was taken to actively track down wanted suspects once their details had been circulated on the PNC
:: Limited capacity within many forces to manage the risk posed by the most dangerous offenders
:: Neighbourhood policing, described as "the bedrock" of the service, continues to be eroded
:: Gangs of violent and dangerous criminals not formally classified.
HMIC said it was warning for the first time of a national crisis in the shortage of detectives and investigators in many forces.
This was leading to excessive workloads, while complex investigations were being led by those who lacked appropriate experience. In one instance, inspectors saw a uniformed officer investigating rape.
The report highlighted the extent to which forces were not taking inquiries further because the victim did not support police action.
In some areas, more than one in five cases were not investigated fully for this reason and the issue was particularly acute for domestic abuse.
The watchdog examined the effectiveness of forces in England and Wales, and said that most provided a largely good service in keeping people safe and preventing crime.
Overall, one force was judged to be "outstanding", 28 forces were "good", 13 "require improvement" and one was rated "inadequate".
Michael Barton, National Police Chiefs' Council lead for crime operations, noted that the inspection found that most forces were "good overall" but said it was "disappointing" that HMIC also had concerns that some were "falling short".
He cited budget reductions and the loss of thousands of officers and staff, adding: "It's a simple reality that we are required to prioritise more.
"Difficult decisions are being made between resourcing neighbourhood teams, response units, specialist investigations and digital and cyber enabled crime."
Policing minister Brandon Lewis welcomed the report's rating of two-thirds of forces as either good or outstanding, as well as improvements in the response to vulnerable people.
"But a number of forces clearly still have more work to do to ensure they are providing the level of service which communities expect and deserve," he said.
Mr Lewis said the Government has protected police funding, adding: "There can be no excuse for any force that fails to deliver on its obligations – those identified as inadequate or requiring improvement must take HMIC's findings very seriously and I expect to see rapid improvements."