‘Arguido’ means a person suspected of committing a crime by the authorities; the closest English equivalent is ‘formal suspect.’

“The action made by the Portuguese authorities should not be overstated,” Brueckner’s lawyer Friedrich Fuelscher remarked.

“I suppose this is a procedural ruse to prevent the statute of limitations from kicking in in a few days.”

There is a 15-year limit on prosecuting severe crimes in Portugal, which is said to have pushed the country’s police to make the step in order to “keep their options open.”

The action was “probably purely for procedural reasons, to avert a statute of limitations in Portugal,” German prosecutor Hans Christian Wolters told Sky News.

Madeleine has been missing for 15 years, which is the legal limit in Portugal for naming someone a person of interest.

Christian B, a two-time convicted child abuser, is suspected of travelling between Germany and Praia da Luz in a campervan for several years prior to Madeleine’s disappearance.

He is presently serving a seven-year term in Germany for drug offences after being convicted of raping a 72-year-old lady in 2005; he has stated that he previously survived by distributing narcotics.

The rape took place in the same town that Maddie McCann vanished.