Cafe owner Mehmet Ali Deniz also accuses the Met of reneging on a deal to give him a new identity and home which, he says, put his life in danger.
Despite having a contract on his head, the informer has lodged a high court writ against the Met commissioner, Sir John Stevens.
In his writ, Mr Deniz alleges that detectives promised him a £3,000 reward for every kilo of heroin seized. One raid alone is said to have resulted in a haul of 60 kilos of the drug.
After a series of successful raids, police told Mr Deniz that they were concerned for his safety as a result of evidence he gave against members of the Turkish mafia. They advised him to leave his home and cafe business in Bethnal Green and placed him in a safe house in Richmond, Surrey.
Mr Deniz, who also closed his kebab shop in Darlington, Co Durham, claims he never received compensation for the loss of his businesses or the British passport he alleges he was promised.
The writ describes how Mr Deniz contacted the ITV programme Crimestoppers in April 1996 saying he had information about drugs dealers operating in London.
After a series of discussions with detectives, Mr Deniz supplied details of more than 25 criminals believed to be members of the Turkish mafia, and also provided details of a store of illegal weapons and ammunition he says were used in mafia-related murders.
Mr Deniz says he was only paid £5,000 of a promised £20,000 by the Met for information about the heroin dealings of a man named Akhtar, a known criminal included on the force's "most wanted" list. Despite being promised the balance by "a very senior police officer", he never received any further payments.
The writ, served by Mr Deniz's solicitors, Purcell Brown of Edmonton, alleges he assisted in setting up six drugs deals, one of which resulted in the murder of a heroin dealer after he failed to pay for three kilos of heroin he bought.
In another case, on the instructions of police, Mr Deniz acted as an accomplice for a heroin importer and set him up with a deal to supply five kilos of heroin to an undercover detective. The dealer was later jailed and Mr Deniz says he was offered £20,000 for his information.
Police became so concerned for Mr Deniz's safety that they asked him not to return to his home address and to close down his businesses. He alleges that when he complained this would mean losing his livelihood, the Met promised to compensate him.
When he was moved to a safe house in Richmond a criminal justice protection unit officer said he would be provided with a new name, a British passport, proper financial reward and permanent secure accommodation. He was told the process would take three to four months.
The writ adds: "The defendant was negligent in failing to give the claimant the proper care and support reasonably expected for a police informant giving information on the dealing and importation of heroin and the use, sale and importation of firearms."
Last night a Scotland Yard spokeswoman said: "We can confirm that Mehmet Ali Deniz has commenced civil proceedings against the commissioner.
"We are not prepared to discuss it further."
In April, a high court judge ruled that supergrasses who claim they have been short-changed in rewards paid for information have no legal right to sue. The judgment came in a case launched by the informant Keith Robinson, who claimed £33,574 plus interest against the commissioners of customs and excise for breach of an alleged contract under which he said he was promised reasonable remuneration and expenses.
Mr Justice Douglas Brown held that no contract existed and that, in any event, on grounds of public policy, "an informant cannot maintain a claim against the commissioners or indeed a chief officer of police in respect of any reward for information supplied".