Only 30% of the 836,131 crimes reported to Lancashire police between 2002 and 2008 have been resolved.

But one of the county's top cops today said the force was hitting targets and it was almost impossible to get to the bottom of every offence.

The figures include all infringements reported to officers – ranging from minor crimes like petty vandalism and theft to armed robberies and gun crimes.

And experts say there has been an increase of smaller, hard to detect, offences like theft because of the impact of the credit crunch.

South Ribble Chief Supt Irene Curtis said: "There will always be crimes where we have very few leads and rely heavily on public support. What we try to do is be up front with people as to what the chances are of us detecting the crime.

"We will always try to, but some crimes are harder to detect. The primary focus is preventing crime and we have had some massive success in that area over the past few years."

But for every crime there is a victim including grandmother Joan Dolan, who was terrified when a robber with a knife burst into the store she was working at and threatened her.

The raider, who swore at 62-year-old Mrs Dolan and demanded money, eventually fled empty-handed after the shop worker locked herself in an office behind the counter.

She was back at work at the Harewood Road Co-Op store, in Deepdale, Preston, almost immediately, but the incident in February left her badly shaken. Eight months on, the offender is still at large.

Mrs Dolan, who is a mother of five and a grandmother of 11, said today: "They (the police) got in touch a few weeks later but since then they have not. They haven't caught anybody".

While she is now over the attempted robbery, Mrs Dolan admits she would feel "a lot safer" if she knew her assailant was off the streets. Home Office figures show of the crimes reported to police, 577,869 have not been solved.

But crime detection rates have climbed steadily since 2002, when 27% of offences were solved. In the past year, 35% of crimes have been detected – above the force's 30% target.

And there has been a steady decrease in the number of crimes recorded by police – down from 130,507 in 2002/3 to 123,681 in the past 12 months.

Unsolved crimes currently on file include a ramraid at a Fulwood off licence in May this year, a terrifying knife point robbery in February which left a shopkeeper in Deepdale badly shaken, to a plague of shoplifting offences, which the Evening Post highlighted earlier this year by publishing CCTV footage of suspected offenders.