German media have named the new suspect in Madeline McCann's disappearance and say they are treating it as a murder investigation.
Madeleine, from Rothley in Leicestershire, has been missing for 13 years.
Video report by ITV News Correspondent Rebecca Barry
Who is the suspect?
The 43-year-old German man, who has been named by the German media as Christian B, is currently serving a prison sentence for a sex crime and has two previous convictions for “sexual contact with girls”.
The man is described as white with short blond hair, possibly fair, and about 6ft tall with a slim build.
None of these convictions are thought to have any links to the disappearance of three-year-old Madeleine in Portugal in 2007.
What German police have said
German police are treating her disappearance as a murder investigation.
They have not ruled out a sexual motive, but added that the suspect may have broken into an apartment in the Ocean Club complex in Praia da Luz – where Madeleine was on holiday with her parents, Kate and Gerry McCann, and her twin siblings Sean and Amelie – before spontaneously kidnapping her.
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.
A statement from German authorities added there is evidence to suggest either a dark coloured Jaguar XJR 6 or a white and yellow early 1980s VW T3 Westfalia was used to commit the crime.
In addition, there is information suggesting that he also earned his living by committing criminal offences, such as burglaries of hotel complexes and holiday flats as well as trafficking in narcotic drugs.
The BKA statement added officers believe others could have “concrete knowledge” of the crime.
What UK police have said
The Met’s Operation Grange, launched in 2013, has always considered the case a missing person inquiry.
Police say a half-hour phone call was made from the suspect's Portuguese mobile phone between 7.30pm and 8pm, around an hour before Madeleine is believed to have gone missing.
Scotland Yard said the man 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.
The Jaguar had a German number plate and was 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.
Police are appealing for anyone who may have seen the camper van in or around Praia da Luz on the night Madeleine went missing, the days before or weeks after, to contact them.
Both vehicles have been seized by German police.
Det Chief Insp Mark Cranwell, who is leading the Met's investigation, told reporters on Wednesday he was taking the “really 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, starting at 7.32pm and ending at 8.02pm on the night of May 3, 2007.
The caller, who is not thought to have been in the Praia da Luz area, is not being treated as a suspect, but is said to be a “key witness” in the case.
“Any information in relation to these mobile numbers during the spring and summer of 2007 could be critical to this investigation,” said Mr Cranwell.
What Madeleine’s parents have said
A statement from Madeleine’s parents, read by Det Chief Insp Cranwell said:
We welcome the appeal today regarding the disappearance of our daughter Madeleine.