A sex offender who changed the registration on his car a day after Madeleine McCann went missing is being considered a key suspect in the likely abduction of the British girl.

It has been 13 years and one month since three-year-old Madeleine disappeared from a Portugal apartment while her parents were out for dinner during their family holiday.

In a major development, British police have a “significant line of inquiry” after tracing some of the movements of a German man who was travelling along the Algarve coast in May 2007.

German police told local ZDF TV station the suspect, whose name has not been released, is a known sex offender in prison for sex crimes.

Christian Hoppe of Germany’s Federal Criminal Police Office said the man had two previous convictions for “sexual contact with girls”.

Officers have seized two cars linked to the 43-year-old.

A 1993 Jaguar XJR6 that has been linked to the suspect. Photo: British Police

Scotland Yard revealed on Thursday morning (Australian time) that on May 3, 2007 – the night Madeleine was last seen – the man made phone calls in the Praia da Luz area where the McCann family was holidaying.

They said he had been driving a VW campervan in the tourist region and also owned a 1993 Jaguar XJR6 with a German number plate. It had been seen in Praia da Luz and surrounding areas in 2006 and 2007.

The day after Madeleine went missing, the suspect arranged for the car to be re-registered in Germany under someone else’s name.

Detectives involved in ‘Operation Grange‘ also revealed:

• The man is in prison for an unrelated matter.
• He is white and in 2007 is believed to have had short blond hair, possibly fair. He was about 180 centimetres tall, with a slim build.
• He lived on the Algarve coast from 1995-2007. He is connected to the area of Praia da Luz and surrounding regions, and spent some short spells in Germany.
• A half-hour phone call was made to the German man’s Portuguese mobile phone at 7.32pm on May 3, 2007 – about an hour before Madeleine is believed to have gone missing.
• Investigators believe the person who made this call is a “highly significant witness” but they have not been able to identify the caller.
• They need information from anyone who might have seen the man in the area or know who he spoke to on the phone that night.

In a statement read by Detective Chief Inspector Mark Cranwell, Madeleine’s parents welcomed the new police appeal.

“All we have ever wanted is to find her, uncover the truth and bring those responsible to justice,” the McCanns said.

We will never give up hope of finding Madeleine alive, but whatever the outcome may be, we need to know as we need to find peace.’’

Madeleine was on holiday with her parents Kate and Gerry McCann and her twin siblings Sean and Amelie when she disappeared from her hotel bedroom.

Police initially suspected Mr and Mrs McCann but later concluded the three-year-old was kidnapped by someone outside of the family.

The German man travelled Portugal in this VW T3 Westfalia campervan in 2007. Photo: British Police 

Scotland Yard is launching a joint appeal with the Federal Criminal Police Office of Germany (BKA) and the Portuguese Policia Judiciaria (PJ), including an £20,000 ($A36,000) reward for information leading to the conviction of the person responsible for Madeleine’s disappearance.

The Met’s investigation has identified more than 600 people as potentially significant.

They were tipped off about the German national, already known to detectives, following a 2017 appeal.

“Following the 10-year anniversary, the Met received information about a German man who was known to have been in and around Praia da Luz,” Inspector Cranwell said.

“The Met conducted a number of inquiries and in November 2017 engaged with the BKA, who agreed to work with the Met.

“Since then a huge amount of work has taken place by both the Met, the BKA and the Polícia Judiciária.

“While this male is a suspect, we retain an open mind as to his involvement and this remains a missing person inquiry.

“Our job as detectives is to follow the evidence, maintain an open mind and establish what happened on that day in May 2007.

“Please contact us without delay so we can get answers for Madeleine’s family.”

Police also took the unusual step of releasing two mobile phone numbers as part of the appeal.

The first, (+351) 912 730 680, is believed to have been used by the suspect, and received a call from another Portuguese mobile, (+351) 916 510 683, while in the Praia da Luz area on the night of May 3, 2007.