It is understood that police both in the UK and Germany have interviewed the suspect in jail but that he has declined to help with their inquiries.
Although some details of the man have been released, British officers stopped short of naming him because, according to sources, it would be a breach of German privacy laws preventing the identification of suspects. The Met Police are working with Federal Criminal Police Office of Germany (BKA).
In a statement, Kate and Gerry McCann said: “We welcome the appeal today regarding the disappearance of our daughter, Madeleine.
“We would like to thank the police forces involved for their continued efforts in the search for Madeleine.
“All we have ever wanted is to find her, uncover the truth and bring those responsible to justice. 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.
“We will be making no further comment regarding the appeal today.
“We would like to thank the general public for their ongoing support and encourage anyone who has information directly related to the appeal, to contact the police. Thank you.”
The appeal for information on the German prisoner was made by Deputy Assistant Commissioner Stuart Cundy and Detective Chief Inspector Mark Cranwell, the senior investigating officer running Operation Grange, the unit set up by the Metropolitan Police to investigate Madeleine’s disappearance.
Police said the German suspect was brought to their attention in May 2017 following an appeal by Scotland Yard made on the tenth anniversary of Madeleine's disappearance.
Detective Chief Inspector Mark Cranwell, who leads Operation Grange, said: “It’s more than 13 years since Madeleine went missing and none of us can imagine what it must be like for her family, not knowing what happened or where she is.
“Following the ten-year anniversary, the Met received information about a German man who was known to have been in and around Praia da Luz. We have been working with colleagues in Germany and Portugal and this man is a suspect in Madeleine’s disappearance.
“The Met conducted a number of enquiries 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.”
Police appeal for help
Deputy Assistant Commissioner Stuart Cundy said: “Madeleine’s disappearance has attracted huge international interest. We are appealing for the public to help us establish what happened.
“We are committed to do everything we can to establish what happened and to find Madeleine.”
An appeal for more information on the German suspects movements in Praia da Luz and for other offences in Germany was due to be made on German television on Wednesday evening.
The German national is known to have been in and around Praia da Luz on the Algarve coast at the time Madeleine vanished on May 3 2007 while on holiday with her parents, Kate and Gerry McCann, and her twin siblings Sean and Amelie.
The suspect, who is in prison in Germany for an unrelated matter, has been linked to an early 1980s camper van - with a white upper body and yellow skirting, registered in Portugal - which was pictured in the Algarve in 2007.
Scotland Yard said he was driving the vehicle in the Praia da Luz area in the days before Madeleine's disappearance and is believed to have been living in it for days or weeks before and after May 3.
He has also been linked to a 1993 Jaguar XJR6 with a German number plate seen in Praia da Luz and surrounding areas in 2006 and 2007.
The day after Madeleine went missing, the suspect got the car re-registered in Germany under someone else's name, although it is believed the vehicle was still in Portugal.
Both vehicles have been seized by German police.
Scotland Yard have identified a German man as the main suspect in the disappearance of Madeleine McCann.
Senior police officers described the breakthrough as "significant" as they appealed for information over the whereabouts of the 43-year-old at the time Madeleine went missing in May 2007.
Friends of Kate and Gerry McCann said it was the biggest development in the case since their little girl went missing in 2007 and the first time that two separate forces - in Britain and in Germany - had publicly identified a suspect.
In a statement the girl’s parents said all they wanted to do was “uncover the truth”.
British police declined to say why the German national was in jail.
In a statement Scotland Yard said: “Met detectives working with German authorities have identified a man currently imprisoned in Germany as a suspect in Madeleine’s disappearance.
“This man is white and in 2007 is believed to have had short blond hair, possibly fair. He was about 6ft in height with a slim build. He is 43-years-old, but in 2007 may have looked between 25 to early 30s.
“We have established that he lived on and off in the Algarve between 1995 and 2007. He is connected to the area of Praia da Luz and surrounding regions, and spent some short spells in Germany.
This individual, who we will not identify, is currently in prison in Germany for an unrelated matter.”
The man, who was 30 at the time, was living in a camper van in the Algarve in Portugal and had received a 30-minute phone call in Praia da Luz, the resort where the McCanns were on holiday, just an hour before the three-year-old girl vanished.
The Metropolitan Police also took the highly unusual step last night of releasing the Portuguese mobile phone number the suspect was using at the time and the number of the person who called him in an attempt to further learn of his movements. Police are trying to discover who called the man.
The suspect also owned a 1993 Jaguar saloon car which, the day after Madeleine went missing on May 4 2007, he re-registered in Germany and under another person’s name.
Scotland Yard released photographs of both the distinctive VW campervan and the Jaguar, pictured below.