“It would have served as the basis of an arrest warrant that could have prevented the attack.”

But there was a second version of the report in which Amri’s involvement was downplayed. “This version no longer refers to professional and organised trafficking, but only to drug dealing,” Mr Geisel said.

Crucially, the minister said the second version of the report was drawn up on Januray 17 — almost a month after the attacks — but “clearly backdated to November 1”.

Mr Geisel has filed criminal charges against two officers in the Landeskriminalamt, the Berlin police equivalent of CID.

There has already been public anger that police and intelligence agencies were unable to identify the threat from Amri, a rejected Tunisian asylum-seeker, despite a trail of evidence linking him to extremist circles and tip-offs from informants that he had talked of carrying out an attack.

But if it now transpires Berlin police missed the chance to take him off the streets six weeks before the attack it will raise serious questions.

“This is a new dimension. It would be devastating if a chance for an arrest was missed,” Burkard Dregger, a high-profile regional MP from Angela Merkel’s Christian Democrats (CDU) said.