Madeleine McCann's parents lose appeal

The parents of Madeleine McCann have lost their appeal against a former Portuguese detective who alleged they were involved in her disappearance.

The parents of Madeleine McCann have lost their appeal against an author of a book about her. (AAP)

Portugal's Supreme Court has ruled that missing British girl Madeleine McCann's parents can't sue for libel a former Portuguese detective who published a book alleging they were involved in their daughter's disappearance.

A court official said that Portugal's highest court ruled the allegations are protected by freedom of expression laws and weren't abusive.

The official spoke on condition of anonymity because the decision hadn't yet been published.

A Lisbon court in 2015 ordered Goncalo Amaral to pay Kate and Gerry McCann 500,000 euros in compensation. The McCanns had sought 1.2 million euros

An appeals court last year overturned that conviction before reaching Portugal's top court.

Madeleine disappeared from a vacation home in Portugal's Algarve region in May 2007, days before her 4th birthday.