A group of well-to-do pensioners who lost their savings in the credit crunch staged an arthritic revenge attack and held their terrified financial adviser to ransom, prosecutors said yesterday.

The alleged kidnapping is the latest example of what is being dubbed “silver crime” — the violent backlash of pensioners who feel cheated by the world.

“As I was letting myself into my front door I was assaulted from behind and hit hard,” the financial adviser James Amburn, a 56-year-old German-American, said. “Then they bound me with masking tape until I looked like a mummy. I thought I was a dead man.”

He was freed by 40 heavily armed policemen from the counter-terrorist unit last Saturday. The frightened consultant was in his underwear, his body lacerated by wounds allegedly inflicted by angry pensioners.

It appears that two couples had entrusted Mr Amburn’s investment company with €2.4 million (£2 million), which he ploughed into Florida’s boom-and-bust property market. The properties became forfeit during the sub-prime mortgage crisis but the couples wanted their money back.

After being bundled into the boot of an Audi in the west German town of Speyer, Mr Amburn was driven southwards to Chieming, close to the Austrian border, where one of the couples Roland K, and his wife, Sieglinde, 79, had a holiday home.

The financial adviser claims he was held there in a cellar for four days almost naked, fed soup twice a day and beaten. Another couple, Gerhard F, 63, and his wife, Iris, 66, both retired doctors, allegedly helped to torture the prisoner.

“I was beaten. They threatened again and again to kill me,” Mr Amburn said. At least two of his ribs were fractured.

Mr Amburn says he tried to escape once when he was permitted to smoke in the garden. He scaled the wall and ran though the rain in his underpants calling for help.

The pensioners pursued him in their car, shouting: “Stop that man! He’s a burglar!” Two locals pinned him to the pavement and he was taken back to the cellar, where he claims he received another beating.

The investment consultant’s break came when he was allowed to send a fax to a Swiss bank asking for the transfer of the funds demanded by the gang.

On the fax he pretended to refer to call options and to insurance policies (the German word for a financial policy is police). This came out as “call.pol-ice.”

“They didn’t notice it but someone at the bank was bright enough to spot it,” Mr Amburn said.

The pensioners are under arrest on suspicion of deprivation of liberty, torture and inflicting grievous bodily harm. These charges carry a maximum of 15 years in prison.

“They were angry because they invested money in propertites in Florida and he lost it all,” Volker Ziegler, chief public prosecutor in Traunstein, said.

The numbers of attacks by elderly people had been rising fast even before the financial crisis hit savings. A three-man gang of pensioners is serving long jail terms for mounting 14 bank robberies across Germany to boost their retirement funds.

Rudolf Richter and brothers Wilfried and Lothar Ackermann were entitled only to modest state pensions of between €100 and €400 a month.

They became enraged by the size of bankers’ bonuses and over nine years — ending in their arrest in 2005 — netted more than €1.3 million. Police recovered only half that sum.

“It is unbelievable how easy it is to rob a bank,” Wilfried Ackermann, 73, boasted during the trial. The men held carrots in their pockets pretending that they had pistols.

On one of the raids Richter, 74, slipped on an icy pavement, dropped the loot and had to be carried to the getaway car.

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