The county comes third in the league table of England and Wales with a total of 1,554 offenders convicted of serious offences living here.
That works out at an average of 122 offenders per 100,000 population – well above the national average of 92 and ahead of other major areas like Greater Manchester and Merseyside.
The reason for the high numbers is unclear. One theory is that low-cost housing in some areas makes it easier to set up accommodation but justice bosses said they tend to return to their home area on release.
The figures come from the Multi-Agency Public Protection Arrangements (MAPPA), a Ministry of Justice scheme which requires violent and sexual offenders to be monitored on their release from prison.
Clive Grunshaw, Lancashire’s Police and Crime Commissioner, said today: “The issue is not how many sex offenders there are in an area, it is how well they are monitored and managed.
“There is a multi-agency responsibility for this and Lancashire Constabulary is playing its part in keeping residents safe from harm.”
The latest figures, for 2013/14, show Teesside and Humberside both house the most Category One sex offenders, with 127 per 100,000 people.
Det Ch Insp Claire McEnery from Lancashire Constabulary’s Public Protection Unit said rigorous checks were in place to monitor released prisoners.
She said: “In Lancashire, there are two Dangerous and Sex Offenders (DASO) teams that consist of specialist police officers and staff who lead the management of sexual offenders in our communities.
“In addition, those considered to be of a certain level of risk are managed by various agencies including the police, probation, and the prison service through MAPPA.
“Eligible MAPPA offenders are identified and information about them is shared by the agencies in order to inform the risk assessments and risk management plans of those managing or supervising them.”
Mick Gradwell, a former detective superintendent with Lancashire Police, said he could only speculate on the reasons certain areas had higher concentrations of offenders.
He felt that a lot of it was down to cheaper house prices in the north – and also the fact that offenders may want to “disappear” in busy towns. Ex-inmates may also have to live off drastically reduced income.
Mr Gradwell said offenders were often directed to houses of multiple occupation. He said: “A lot of these people are rehoused where property is cheaper and it is easier to ‘hide’ these hostels in certain areas.”
Mr Gradwell said the figures highlight the “stresses and strains” the authorities — including police, probation and councils — face monitoring people in these “hotspots”.
He added: “In the north, the figures are showing there are quite a number of hotspots for category one sex offenders.
“It is not something the police want to publicise because if you start highlighting a particular area as having a high number of people living there, it creates problems.”
Lancashire is followed in the league table by West Yorkshire which has 110, and Greater Manchester was fifth with 107, while Derbyshire also had 107.
By contrast Surrey has just 55 serious sex offenders per 100,000 people, Thames Valley has 61 and Hertfordshire has 63.
A Ministry of Justice spokesman said: “Most offenders are returned to their home area when released.
“Sex offenders on licence are subject to strict conditions to help prevent reoffending and protect the public. These include exclusion zones, non-contact orders and sex offender treatment programmes, as well as being subject to the sex offenders’ register. If they fail to comply, they can be recalled to prison.
“We have tough measures to manage sex offenders in the community, and these work to prevent reoffending and protect the public.”
Category One offenders are registered sexual offenders who are equired to notify the police of their name, address and other personal details, including if they move.