An immigration officer who admitted issuing visas to scores of immigrants not entitled to stay in the UK has been jailed for seven years.
Samuel Shoyeju, 53, of Namur Road, Canvey Island, Essex, admitted misconduct in a public office at Basildon Crown Court.
He wrongly granted leave to remain to 44 non-EU residents while working for the UK Border Agency.
Only 14 of the false letters that he issued have been recovered.
Judge Christopher Mitchell said the case threatened to undermine the hard-won reputation for "probity and honesty" of British civil servants.
'Not all traced'
He added: "Actions like yours call into question in the public mind the entire integrity of the immigration system when, at the present time, immigration and immigration decisions are extremely sensitive."
Basildon Crown Court heard the "treasured status" allowed immigrants to live, work and claim benefits as well as applying for full British citizenship.
The recipients, who are all believed to be Nigerian, ranged from asylum seekers to those who were identified as "overstayers".
Prosecutor Lucy Kennedy said: "Not all of those people have been traced."
Shoyeju, who worked as a line manager in Croydon, amended and destroyed electronic and paper records to cover his tracks.
He admitted misconduct in public office by falsely granting indefinite leave to remain between 2006 and 2007.
Although the prosecution has not been able to prove a financial motive, the court heard thousands of pounds were paid into his bank account during the time of the offence.
Stephen Linehan QC, in mitigation, said that there was not sufficient evidence that Shoyeju had a financial motive and could not be sentenced on that basis.
Shoyeju arrived in the UK in 1988 and was granted indefinite leave to remain as the spouse of a British citizen and was granted full citizenship in 1996.
Joe Dugdale, the UK Border Agency's head of human resources, said: "Samuel Shoyeju abused the trust placed in him as a public servant, and the sentence he has been given today reflects the severity of his crimes."