Germany's intelligence service paid over €4m to the informant who tipped them off about former Deutsche Post chief executive Klaus Zumwinkel.

German media reported over the weekend that the BND agency had paid a former employee of LGT, Liechtenstein's largest bank, for an electronic list which is said to hold details of 1,000 alleged tax evaders.

Last Thursday's raid of Zumwinkel's home was believed to be just the tip of the iceberg, and other rich Germans are expected to be targeted in what looks set to be Germany's biggest tax evasion probe ever.

A spokesperson for the finance ministry would not confirm the exact sum paid to the anonymous informant, who is now in protective custody, but commented that the money had been 'well invested'.

Zumwinkel, who resigned from his role at Deutsche, is said to have dodged €1m in taxes alone by transferring funds to the Liechtenstein-based bank, and German authorities are confident of recouping their costs once others on the list have been investigated.

German chancellor Angela Merkel is expected to raise the issue of lax banking practices with Liechtenstein's prime minister Otmar Hasler tomorrow during his visit to Berlin.