Around one in three crimes reported to police are not investigated, figures have revealed.
An investigation by The Times showed for around half of the police forces in England and Wales, about 32% of crimes are dropped from further investigation.
London's Met Police confirmed the figure is higher in the capital - with nearly 44% of crimes "screened out" of further investigation.
Of a total of 824,495 crimes for 2010, 463,315 were "screened in", while 361,180 were "screened out".
According to The Times' report, almost 650,000 out of just over two million crimes were screened out in the past year in 21 of England and Wales' 43 forces.
The numbers were gained from responses to a survey carried out under the Freedom of Information Act.
It is believed cases such as burglary, theft and criminal damage are more likely to be dropped because officers think there is little chance of success and need to focus limited resources elsewhere.
But the Association of Chief Police Officers (ACPO) today said pursuing the investigation of a crime to a successful conclusion was always the police's "preferred outcome".
ACPO lead on crime statistics, deputy chief constable Douglas Paxton, said: "Recent crime data shows that in 2010/11 there were 9.6 million offences in England and Wales.
"When assessing crime we need to look at the likelihood of identifying a suspect for a particular crime. The decision of whether a crime is detectable has got to take into account all evidence available to officers, such as forensics and witness reports."