Child sex offenders are not being monitored properly on their release from prison because there are too many of them, a report found.
The rapidly growing number of people registered as paedophiles threatens to overwhelm resources to manage them, according to Home Office research.
A new study found there is a "severe shortage" of accommodation and supervised housing for sex offenders in some areas.
There are also not enough treatment programmes in parts of England and Wales, with lengthy waiting lists as a result.
The study also highlighted how an increasing number of sex offender cases was not being matched by increased funding.
It found widespread opposition among staff to a US-style Megan's Law, a move towards publicly identifying some sex offenders in the community.
Written by Jason Wood and Hazel Kemshall, of De Montfort University, Leicester, the research is part of a Government review of child sex offender management.
It focussed on how Multi-Agency Public Protection Arrangements (Mappa) in three areas keep the behaviour of offenders under observation.
The report said resource gaps in several areas were seen to be a "hindrance to effective supervision".
It said: "A key concern for areas was how to respond to the inevitable growth in the numbers of offenders subject to registration and there were grave concerns... that resources were not increasing as the registration list does."
