By Kate Dailey

Last week, an English court handed a whole-life sentence to Dale Cregan for murdering four people, including two policewomen.

That penalty means he will never be eligible for release, and it puts him in rare company, making him one of about 50 people in the UK serving such a sentence.

Had he been in the US, he would have been less of an anomaly.

In the US, at least 40,000 people are imprisoned without hope for parole, including 2,500 under the age of 18.

That is just a fraction of those who have been given a life sentence but yet may one day win release. The Sentencing Project, a non-profit organisation that studies sentencing and criminal justice in America, estimated in 2009 that at least 140,000 prisoners in the US now serve a life sentence.

This does not include convicts given extremely long sentences with a fixed term, like the Alabama man sentenced to 200 years for kidnapping and armed robbery.

Most of them will have the opportunity for parole – though Sentencing Project Director Marc Mauer says few will receive it.

David Wilson, professor of criminology at Birmingham City University, says several factors underlie the high number of American convicts imprisoned for life.

“In large part it reflects the overly punitive nature of the American criminal justice system,” says Mauer.

Read More BBC News – Why the US locks up prisoners for life.