The leaked German military phone call which discussed British troops’ involvement in Ukraine could be just “the tip of the iceberg” of lax security in the country, Germany’s former head of intelligence has said.

August Hanning, former president of the German Federal Intelligence Service, warned on Monday that Russians may have access to even more Nato secrets following intelligence agents’ interception of a non-secure phone call between several high-ranking officials in the German armed forces.

Hanning told German outlet Bild “this leak could have just been the tip of the iceberg”, while other sources said Russia was using German Chancellor Olaf Scholz as a “useful idiot” – and had circled Germany as Nato’s “weakest link”.

It has been a testing week for Scholz; the embarrassment of the leak and the subsequent security concerns it poses follows comments by the chancellor himself that British operatives were on the ground in Ukraine delivering – and training Ukrainian soldiers with – cruise missiles.

Lord Cameron will travel to Berlin this Thursday to discuss the leaks

And Foreign Secretary Lord Cameron is set for crunch talks with his counterpart in Berlin this Thursday, with the leaks due to hang over discussions.

But the Foreign Office distanced itself from speculation that Lord Cameron and German Foreign Minister Annalena Baerbock would butt heads in the meeting, saying: “There will be detailed discussions about both the big issues of the moment: Ukraine and Gaza.”

Downing Street said the leak of British secrets was “a very serious matter”, while a diplomatic source told the Telegraph: “Russia has identified Germany as the weakest link in the alliance and Scholz as a useful idiot to take Germany out of the equation.

“And [Russia] might not be wrong, given the way he positions Germany and his party in this debate.”