Three former Scotland Yard police officers and a serving detective have been arrested as part of an investigation into allegations that members of the force's anti-corruption unit were paid thousands of pounds in bribes.

The Metropolitan police said the 45-year-old male detective was arrested on suspicion of receiving payments for information at a residential address outside London.

Two of the former police officers, men aged 53 and 58, were arrested during raids at a business address in central London. The pair were arrested on suspicion of bribery of a police officer and remain in custody.

The third former police officer attended a south London police station by appointment and was also arrested on suspicion of bribery of a police officer. He also remains in custody.

A Scotland Yard source with knowledge of the arrests confirmed the central London premises raided this morning belonged to RISC Management, a firm of private investigators that was working for a notorious Nigerian fraudster, James Ibori. The arrested 53-year-old was understood, the source said, to be Keith Hunter, the chief executive of RISC Management and a former Met detective.

The Guardian revealed on Tuesday that the Met was investigating allegations RISC Management may have paid bribes to police officers in the Met's proceeds of corruption unit.

Ibori was recently jailed after pleading guilty in the UK to laundering £150m. He was under investigation by the Met anti-corruption unit around the time RISC Management is alleged to have made the payments.

Hunter, from Banstead in Surrey, claims to have worked on "high-profile investigations of national and international organised crime" at Scotland Yard before entering the private investigations industry in 1997.

Prior to his arrest, Hunter denied allegations of wrongdoing, telling the Guardian: "RISC management does not need to pay serving police officers for confidential information as we pride ourselves on our ability to provide positive solutions and accurate information legitimately. RISC Management has a highly respected reputation for conducting professional investigations."

Hunter added that his company was "proud to have a network of highly professional consultants, contacts and resources". He said: "These individuals are hired precisely because of their unique skill set and expertise."

The identity of the second former Met police officer to be arrested along with Hunter was not known.

Details of the case were brought to the attention of parliament on Tuesday when Mike Schwarz, a lawyer for one of Ibori's co-accused, gave evidence to the home affairs select committee about the case.

Schwarz, from Bindmans solicitors, gave details about a set of invoices he said suggested RISC Management had paid around £20,000 to sources close to the police investigation into Ibori.

The committee is holding an inquiry into whether private investigators should be subject to statutory regulation. Schwarz, who represents Bhadresh Gohil, a London-based solicitor jailed along with Ibori for orchestrating his money-laundering scam, told MPs the case amounted to an undetected case of "apparent corruption right at the heart of Scotland Yard".

After the evidence, Hunter accused Schwarz of "grandstanding" in front of the Commons committee, instead of taking the "correct course of reporting the matter to the police". He said Schwarz had not produced any evidence to support his claims and acted for a convicted solicitor, Gohil, who was jailed for seven years for money laundering.

The Met was first made aware of the allegations of bribes in August last year, when the force was anonymously posted the set of invoices referred to in parliament by Schwarz.

It was another three months before the force's directorate of professional standards (DPS), which investigates internal corruption, opened an internal inquiry. This investigation is being supervised by the Independent Police Complaints Commission (IPCC), which had been anonymously posted the documents around the same time.

Until recently, the Met had not contacted RISC Management or interviewed any of the police officers suspected of taking bribes. Last week, the force indicated to the Guardian that it had "uncovered evidence that casts doubt on the credibility" of the allegations against police officers. However, that position changed on Tuesday, when the force issued a statement suggesting new developments in the investigation.

The Met said in its latest statement it is "investigating an allegation that illegal payments were made to police officers for information by a private investigation agency". It added: "Officers from the [DPS] have today executed search warrants at a business address in Conduit Street, London and arrested two men."

The Met added: "Both are at present in custody pending further inquiries. This was a pre-planned operation that forms part of a long and complex investigation by the directorate of professional standards."