More than 400 sex convicts on the streets in North Wales are being monitored by a specialist agency, a government report has revealed.

Police and probation workers were keeping tabs on 418 offenders in the region - 137 by the central division, 101 in the west division, and the remaining 180 in the east. The regional figure shows an increase of four on last year.

The figures were contained in the annual report of the Multi Agency Public Protection Arrangements, known as MAPPA, which is made up of police, prison and probation services.

It was set up eight years ago to ensure sex offenders did not slip through the cracks in the system.

The report showed 30 of those being watched were jailed for breaching their orders and one has been charged with committing a further offence.

Shadow Police Minister David Ruffley warned the increase in numbers would heap more pressure on over-stretched police forces.

He said: "The increase in the number of sex offenders being registered is a sign of progress but it also underlines the need to allow police to do their jobs.

"As a result of this worrying trend there will be pressure on police time to keep an eye on these offenders in local communities.

That is why it is all the more important to cut the amount of police time wasted on unnecessary bureaucracy."

Across England and Wales the number of sex offenders being monitored went up 3% from 31,392 to 32,336.

Justice Minister Maria Eagle said: "The offenders dealt with under MAPPA can display extremely dangerous and unpredictable behaviour so the risk of further offences is ever present.

"That risk can never be eliminated entirely, but the majority of those subject to active MAPPA management do not seriously re-offend due to robust and effective management. The number of those who re-offend seriously has remained at around 0.5% for the past four years."

The Ministry of Justice is now piloting lie-detector tests as part of the monitoring process.

Paul West, ACPO (Association of Chief Police Officers) spokesman on sex offenders, said: "Protecting the public from those sexual offenders and violent offenders who pose a risk of serious harm is a key role for the police service; however, we recognise that this cannot be achieved by any one agency working alone.

"The risks posed to the public by such offenders can never be completely eliminated, but the reports provide evidence that MAPPA successfully keeps them to a minimum and enhances public safety."