The head of counter-fraud at Oxfam plundered more than £64,000 from the charity after he became addicted to prescription painkillers, the Old Bailey heard today.

Edward McKenzie-Green, 34, created invoices for companies he had set up and then paid the cash into bank accounts including his father's.

The fraud expert had become paranoid through his use of drugs and stockpiled £64,612 for the moment he was going to be fired by the world renowned charity.

After McKenzie-Green pleaded guilty to fraud, a money laundering charge was dropped against his father, Edward Green, 62.

McKenzie-Green was released on bail ahead of sentence, but warned by Judge Timothy Pontius: "Because of the amount of money involved and the circumstances in which the fraud was carried out, a prison sentence is a likelihood."

He hung his head in the dock and appeared to wipe away a tear during the hearing.

McKenzie-Green submitted the false invoices himself and because of his position he could ensure they were paid, the court heard.

The companies were firms that he had set up and controlled and the cash was paid either his father's bank account or that of a friend.

McKenzie-Green even invented a character called Keith Prowse who corresponded with Oxfam to explain why the payments had to be made.

His barrister Matthew Sherrat told the court: "During the period up to January 2014 the defendant had a very serious addiction to prescription medication.

"At the same time his marriage, which he was attempting to hold together was failing.

"He was involved in quite a high pressure job. He had a very good career and had enjoyed a responsible position.

"He suffered a break down-and was moved to a psychiatric hospital."

Mr Sherrat said McKenzie-Green had been 'paranoid' and was treated in hospital for a month.

"He was putting money aside effectively in the expectation of losing his job," the barrister added.

The judge agreed to adjourn the case so that psychiatric reports can be prepared.

"It is essential the court knows more about the mental health difficulties," the judge said.

Father-of-one McKenzie-Green, of The Leys, Chipping Norton, has no previous convictions.

He admitted fraud by abuse of position and a charge of theft of a laptop computer was dropped.

His father, of Scott Crescent, Cumbernauld, Glasgow, was cleared of concealing criminal property between February 1 and December 1, 2011.

McKenzie-Green will be sentenced on May 16.