The head of Britain's second largest police force has admitted that six in every 10 crimes reported in his jurisdiction were not investigated.

Sir Peter Fahy, chief constable of Greater Manchester Police, defended his controversial policy by saying that smarter policing strategies had led to a fall in crime.

Manchester officers targeted a small core of known, persistent offenders responsible for the majority of crimes, he said.

"We balance between investigating offences after they have happened and targeting those who we know are out there every day, looking for criminal opportunities," he said.

Police budgets have been slashed by 20% in real terms by 2015.

Fahy, vice-president of the Association of Chief Police Officers, compared his controversial tactics to the way hospitals work.

He said: "In the same way that the health service concentrates on the most serious illnesses and the treatments likely to have most effect, the police have to concentrate on the most serious crimes and those where there are lines of investigation likely to produce evidence of the offender.

"In practice, this translates into about 40% of crime being actively pursued at any time.

"We look at all crimes to identify patterns of offending and to build the picture of where we need to target police patrols. In many crimes there are no witnesses, no CCTV and no forensic opportunities."

Labour's Graham Stringer said that taxpayers expected police to investigate all criminal actions.

"That sounds like bureaucratic gobbledegook. Deprioritising the majority of crime is bound to lead to a loss of confidence in the police force," said Stringer.

"Victims have every right to be angry."

Javed Khan, chief executive of independent charity Victim Support, said: "For victims and the public to have confidence in the police, they need to know that, when they make a report, it will be taken seriously and adequately assessed."

Screening out difficult investigations has become widespread across the UK.

In London, 45% of all crimes, a quarter of robberies, two in five burglaries and three-quarters of car thefts were abandoned at an early stage in 2012.

In total, 346,397 reported crimes were screened out. In Bedfordshire 39% were abandoned discontinued and in Warwickshire the figure was 37%.