Successful companies are bankrupted, sold off and their staff sacked after financial attacks by gangs who seem above the law.

For 10 years Alexei Kurkov worked at a small factory in Moscow making fire-safety equipment. One morning in November 2004 he turned up to work as usual. The doors were locked.

Overnight, his company, Specialist Electrical Equipment, had been taken over. Its new owner was a mysterious firm registered in the British Virgin Islands. The owner promptly sacked all staff. The company's valuable property in Moscow was sold off.

"It was as if we had never existed," Kurkov said. "We took the case to court. But the judge said there was no proof we had worked there.

"Fictional employees had taken our place. We had been replaced by Dead Souls," he said - referring to the Nikolai Gogol novel where dead serfs are included in landowners' accounts.

Kurkov and his co-workers had fallen victim to raiders - criminal gangs who with the assistance of corrupt bureaucrats, policemen and judges have seized assets worth billions of pounds.

In the west, corporate raiders legally take over weak or struggling firms. In Russia, raiders target healthy or successful businesses - bankrupting them artificially and transferring ownership to dubious offshore shell companies.

Last week even BP's chairman Peter Sutherland used the word raiding. BP's Russian partners were trying to seize control of TNK-BP, their troubled joint venture, using dubious 1990s "corporate raiding" practices, he said.

The problem is most acute in Moscow. Raiders working with the connivance of local officials have recently bankrupted Moscow's planetarium - and are threatening two historic houses belonging to artists and sculptors.

Other acquisitions have a surreal flavour. In Kazan, raiders have attacked a firm making orthopaedic legs. And in the Siberian town of Omsk a criminal gang has tried to take over the tank factory. Victims have included river ports and nuclear science institutes.

Rule of law

Dmitry Medvedev - Russia's president - has pledged to wipe out raiding, known by Russians as reiderstvo. Medvedev, a former St Petersburg lawyer, has made it clear he wants to end bureaucratic corruption and what he calls Russia's "legal nihilism". In a speech this month, he suggested that establishing the rule of law was his most urgent task as president. "Our job is to create absolutely independent modern courts," he declared.

Questions remain about whether Medvedev can deliver judicial reform - assuming, that is, he wants to. In the Putin era, the Kremlin famously used the courts to punish its political enemies. Judges unfailingly gave the verdict the state wanted. Individuals who displeased the Kremlin found the law applied to them with pedantic vigour. Favoured defendants didn't need to turn up. What counted wasn't the law but the person it was applied to.

Analysts are sceptical that Medvedev can curb the Kremlin's meddling in judicial affairs. "Russian leaders have been talking about legal reform since the time of Ivan the Terrible," Mikhail Delyagin, the head of Moscow's Institute for Global Problems, told the Guardian. "Putin also talked repeatedly about reform, but the results were the opposite of what he declared. Maybe Medvedev will succeed. But I doubt that Putin's loyal apprentice would wish to correct his master's actions.

"We shouldn't forget that Medvedev was Putin's main lawyer. It was Medvedev who wrote the laws ramping up pressure on the opposition and who ruled out the possibility of legal opposition activity in Russia."

Experts estimate that there are 70,000 cases of raiding in Russia a year - most of them instigated by corrupt senior officials. The standard method is for a company to be hit by a large invented tax bill. The owner is then arrested. While the owner is in prison, raiders using forged documents and shareholder protocols sell the bankrupted company to another firm. By the time the owner emerges the business has been re-sold numerous times.

Yesterday one raider, speaking anonymously, said the profits from raiding were enormous. "It costs around $120,000-$170,000 [£60,000-£85,000] to bankrupt an average company. But you can then make $3-4m profit."

Typically, raiders bribe officials in Russia's equivalent of Companies' House as well as bureaucrats in the agency for property registration and the bureau of land management, he said.

"Basically raiding is robbing. The people who do it are educated and well dressed. They drive good cars. Most importantly, they have a calm head. They already have money but want more." Asked whether he felt guilty, he said: "I feel sorry for the victims."

Cops as robbers

The primary target of the raiders is property. Office rental space in central Moscow costs £1,250 a square metre a year - the second most expensive in the world after the West End of London. In extreme cases, police have been known to arrest owners and release them only after they have signed over property to raiders.

According to researchers, only a handful of cases ever make it to court - a fact that suggests the widespread complicity of law-enforcement agencies and the FSB, Russia's post-Soviet spy agency. The agency is supposed to battle economic crime.

Asked why officials did not intervene, Valeria Filimonova of Moscow's centre for political technologies said: "They are the ones who order the raiders' attacks." They included senior members of the administration, she admitted.

In a recent report, the head of the centre, Igor Bunin, went further. Illegal raids had become "the main problem afflicting the country's economy", he said. His report lists several other recent victims of raiding: Arbat Prestige - Russia's biggest cosmetics chain; an ammonia factory; and Moscow's Domodedovo airport.

Kurkov's woes did not end when his company in the south Moscow suburb of Yasenevo was taken over. The white square building surrounded by 1960s apartment blocks and children's playgrounds now belongs to an internet firm.

Kurkov joined the company in 1995, when it employed about 2,000 people. By 2004 the workforce had shrunk to 100. Its chief accountant then seized the firm with help from a gang of professional raiders, Kurkov says. She refused to pay employees their wages and failed to return their workbooks, necessary to obtain a full pension.

Kurkov and 14 colleagues went to court. But the accountant produced documents showing he had never worked there. The judge mysteriously agreed. "I don't want to say the judge was bribed," Kurkov said. "But what other conclusion could I come to?"

Kurkov said that he had approached unions for help and complained to various ministries. In March, just before the presidential election, he even wrote to Medvedev. His quest for justice got nowhere. Medvedev's office wrote back telling him to get in touch with prosecutors. But prosecutors weren't interested, he said. "Nobody wanted to know. I believe Medvedev is doing his best. But I personify legal nihilism."

Now 68 and retired, Kurkov survives on 5,000 roubles (£110) a month. This is despite the fact that in Soviet times he received a hero of labour medal, for his productivity.

He estimates the shadowy raiders made off with around £15m. "This kind of injustice would have been impossible in the Soviet Union," he said. "In the Soviet Union I was somebody. Now I'm nobody."