A postal worker acted as an insider for Congolese crime bosses to steal £26,000 worth of benefit giros in an elaborate fraud.

And Royal Mail bosses have launched a security review into how the worker and a colleague got jobs at sorting offices, despite being suspected illegal immigrants with police recrods for dishonesty.

Musongi Bacha, 41, who worked at the Burnley delivery office, and Leonardo Seke, 35, were jailed for three-and-a-half years and two-and-a-half years respectively after admitting conspiracy to defraud.

They teamed up with a professional fraudster from the Congo to steal benefits cheques.

Congolese man Kabasu Shambuyi, 36, of London, who masterminded the scam, was sentenced to three-and-a-half years for conspiracy.

Minshull Street Crown Court, Manchester, heard how Bacha and Seke passed the stolen cheques down the criminal chain and the benefit documents were then "cloned" and cashed in at various post offices across Manchester Prosecutor David McLachlan said the gang would add an extra digit to the stolen giros and managed to treble the amount of money cashed in from 366 giros and paid orders between November 2003 and July last year.

As many as 320 of these giros were cashed, earning the gang £91,276, when the actual value of the cashed cheques amounted to just £26,077.

Bacha, who gained a business degree in his native Congo, worked at Burnley delivery office and Sale sorting office without bosses checking that he had cautions for forgery in 1997 and 2001.

Angolan-born Seke, of Hulme, Manchester, worked at the Sale sorting office between October 2004 and March 2005 despite having fraud convictions dating back to 2002.

Judge Jonathan Foster QC said: "These crimes strike at the security and integrity of the postal system. I expressed my surprise that Bacha and Seke were able to obtain employment through agencies without any adequate security checks.

"I have communicated my concern to the Post Office, who have acknowledged that in this case their system was too lax.

"They now have a system of approving agencies and registration of persons who a possible risk, and they have access to criminal records."

Three others admitted conspiracy to defraud and were given community punishments.