A prime suspect in the disappearance of British girl Madeleine McCann has dropped a legal appeal for an early release from prison.

News Christian Brueckner has aborted his parole bid comes as German police dug up a garden near his former home in the northern city of Hannover.

A small excavator was used to clear the allotment plot while several investigators combed through the dirt with rakes and shovels.

The search is part of their investigation into the 2007 disappearance of then three-year-old Madeleine, said a spokeswoman for the prosecutor’s office in Braunschweig.

German Investigators are searching an allotment that belonged to Christian Brueckner. Photo: Getty

The spokeswoman, Julia Meyer, confirmed police investigators had been at the site since Monday with an excavator, but could not give any further details on the procedure.

Police would “still need some more time to finish”, Ms Meyer said.

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There were serious concerns that Brueckner who is in jail for drug offences could have been released as early as this week.

An image supplied by the Carabinieri Milano shows a 2018 police mug shot of Christian Brueckner, where Brueckner was arrested and extradited to Germany.

He had appealed against a conviction for the 2005 rape of a 72-year-old woman at Praia da Luz in Portugal’s Algarve region where Madeleine went missing while on holiday with her family.

German authorities said last month they had identified the 43-year-old German citizen as a suspect in the McCann case and were investigating him on suspicion of murder.

Hans Christian Wolters, who is leading the investigation into Brueckner, previously told the PA news agency that prosecutors have “concrete evidence”, but not “forensic evidence” that Madeleine was killed by the suspect.

The parents of missing girl Madeleine McCann pose in May 2012 with an artist’s impression of how their daughter might look. Photo: Getty

He said they may “know more” than Scotland Yard, who are still treating the case as a missing person investigation.

Brueckner spent many years in Portugal, including in Praia da Luz around the time of McCann’s disappearance, and has two previous convictions for “sexual contact with girls,” authorities have said.

He was last registered living in Germany in the city of Braunschweig, which is about 70 kilometres from Hannover.

-with AAP