Two women who posed as sisters and claimed hundreds of thousands of pounds each in benefits after buying false identities have been jailed.
The pair, known under the assumed names of Antoinette and Louise Kaidi, pleaded guilty six days into their trial in March after the jury were "laughing" at their defence, the court heard.
Antoinette, of Oxford Road, Enfield, qualified as a nurse after using her identity to fund her training, while Louise, of Springfield Road, East Ham, enrolled in a nursing course at London South Bank University.
They were arrested last year and convicted of a total of 23 counts, dated between 2003 and 2015, including fraud, conspiracy to assist in unlawful immigration and dishonesty in making a false statement or representation with a view to obtaining benefit.
Sentencing them each to 33 months in prison His Honour Judge John Tanzer told them their crimes were of a serious nature.
He said: "These are not victimless offences. They are offences the community feels very strongly about."
He said the convictions were part of a wider probe into other people, adding: "I was told all of this is part of a very large investigation involving some £4 million."
The Kaidis were convicted of taking thousands of pounds from the NHS in training and bursary costs, as well as from the Department of Work and Pensions in false tax credit and income support payments after assuming so-called "ghost identities".
Louise claimed in the region of £270,000 while Antoinette obtained £290,000, which included her earnings while working as a nurse.
Both women claimed to be from Togo but it is believed Antoinette is of mixed Nigerian-Ghanaian heritage, while Louise is Ugandan, although prosecutor Caoimhe Daly admitted the true identities of the women are still unknown.
Judge Tanzer said the women admitted their crimes in the face of a jury who did not appear to believe their stories.
Addressing the women he said: "Antoinette you were giving evidence with a jury laughing at the attempts by you to say that you were not aware of your real identity."
Both Antoinette, a mother-of-two, and Louise, a single mother-of-three, cried as they sat in the dock at Croydon Crown Court.
Sara Braker, criminal investigator at the Department for Work and Pensions, said: "We worked closely with NHS Protect on this case to bring these criminals to justice.
"We know it's only a small minority of people who commit benefit fraud, but our investigators work tirelessly to root out those who are out to steal from taxpayers."