DOZENS of freed sex offenders including child rapists have been sent back to prison after failing lie detector tests.

Almost 1,500 were hooked up to polygraphs to ensure they were sticking to release terms and were not a danger.

And in 45 cases of the lie detector sessions, the sex offenders’ responses triggered alerts to probation officers - who then recommended them to be locked back up.

They include child rapists and paedophiles found to have been looking at online child abuse images after being hooked up to the machines.

Our Freedom of Information probe shows those caught out by lie detectors include sex offenders originally jailed for the rape of boy under 13, the attempted rape of a underage girl and unlawful intercourse with an underage girl.

A total of 1,478 freed prisoners underwent lie detector sessions from the scheme’s August 2014 launch to July 2017 - the latest available figures.

Lie detector testing is now mandatory for high-risk sex offenders.

David Spencer, of the Centre for Crime Prevention, said: “It is imperative serious sex offenders are only let back into the community when there is absolutely no chance that they pose a risk to the public. At present, that is clearly not the case.”