The Metropolitan Police said new guidelines would mean officers could “determine very quickly if it is proportionate” to investigate “lower level, higher volume offences” further.
Deputy Assistant Commissioner Mark Simmons said the force had to work with fewer officers and less money, with the Crime Assessment Policy introduced to help prioritise resources.
However, he maintained that serious crimes would always be investigated.
He said: “Of course we are not talking about things like homicide, kidnap, sexual offences, hate crime or domestic violence, but the lower level, higher volume offences such as shoplifting, car crime and criminal damage.
“This is not to say these cases will not be investigated further, however by applying the assessment policy we will be able to determine very quickly if it is proportionate to do so.”
Mr Simmons said that the pressure on police resources meant it was “not practical” to use up resources on lower-level crimes.
He added: “Clearly this is not about letting criminals get away with crime, or not investigating the cases we are solving at the moment, if we thought it was, we simply would not do this.
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“With the pressure on our resources it is not practical for our officers to spend a considerable amount of time looking into something where for example, the value of damage or the item stolen is under £50, or the victim is not willing to support a prosecution.
“We need our officers to be focused on serious crime and cases where there is a realistic chance that we will be able to solve it.”
Under the new policy 150,000 fewer offences will be investigated every year, according to reports.
Ex-Met detective chief inspector Mick Neville told the Sun: “This is justice dreamed up by bean counters in shiny suit land.
“No consideration is being given to victims. The new principles will focus police attention on easy crimes where there is a known suspect.
“Few professional criminals target people who know them, so the worst villains will evade justice.
“Not investigating high volume crimes like shoplifting with a loss of under £50 will give junkies a green light to thieve.”