A civil servant and her taxi driver lover who conned the Crown Prosecution Service (CPS) out of £1 million in a "colossal" expenses fraud have both been jailed for six years.

CPS area manager Lisa Burrows and cabbie Tahir Mahmood "operated as a team" to rake in £4,000 a week over five years by lodging claims for non-existent taxi journeys.

The pair used the proceeds of the fraud to fund luxury holidays to Dubai and New York, as well as splashing out on designer handbags, clothing and jewellery, Birmingham Crown Court heard.

Detailed investigations into the fraud, which went unnoticed despite four annual audits, have failed to trace more than £660,000 of stolen public funds.

But inquiries conducted by financial investigators did establish that Burrows, who earned £24,000 as a regional finance manager, was able to spend almost £250,000 on her Marks & Spencer credit card during the fraud.

Burrows, 42, of Titford Road, Oldbury, West Midlands, and Mahmood, 50, of Eastbourne Avenue, Hodge Hill, Birmingham, pleaded guilty to conspiracy to defraud shortly after their arrest in February this year.

Opening the facts of the case, prosecutor Brian Dean said Burrows, who worked at CPS offices in Birmingham, began the fraud in 2008 shortly after meeting Mahmood.

Burrows, who later got the taxi driver a job as an apprentice with the CPS, submitted bogus invoices for a total of £1,021,475 between early 2008 and Ferbuary 2013.

Mahmoood, who "held the purse strings" in the fraud, set up a bank account in a false name to receive payments to a fictitious taxi firm.

Mr Dean told the court: "Burrows identified that the CPS spent considerable sums on the provision of taxis.

"She then decided, along with Mr Mahmood, to exploit that by making false claims for non-existent journeys.

"Mahmood played a full and significant role in the conspiracy in the initial planning of the fraud and by ensuring that they could get their hands on the money in cash form by setting up bank accounts in false names.

"He withdrew nearly £1 million in cash over five years, most of which is still unaccounted for."

Mahmood, dressed in a casual suit, and Burrows, wearing a dark jacket, showed no emotion as the court heard how they handed over £8,000 of public money to pay for a single visit to a New York hotel.

Cash from the fraud was also spent on a stay at Dubai's landmark Jumeirah Beach Hotel and funded purchases from high-end shops including Bloomingdale's.

After their arrest, the fraudsters admitted that the name of their fictitious cab firm, B&M Taxis, stood for Burrows and Mahmood.

Mahmood told police he had used £20,000 as a deposit to buy a house and had holidayed in Spain and Dubai, once spending £10,000 during a week away.

Meanwhile, Burrows, who worked for the CPS for more than 20 years, told detectives she had given Mahmood legitimate taxi work after meeting him in an internet chatroom.

She claimed her lover had then suggested the fraud, which "escalated" as she treated herself to designer items made by Abercrombie and Fitch, Prada and Tiffany.

Passing sentence, Judge William Davis QC described the planned and persistent fraud as a gross abuse of a position of trust.

The judge said: "It is difficult to imagine a more serious fraud of its type.

"It was you, Burrows, who created and then authorised the payment of the bogus invoices. You knew how the system worked.

"Over the course of five years you, Burrows, paid into your bank account over £320,000 in cash, all of which must have been the proceeds of the fraud.

"That money went on high living - expensive holidays in Dubai and New York, designer clothing, jewellery. What happened to the rest of the money - some £664,000 - is not known save that it was you, Mahmood, who withdrew the money in cash.

"The fact that the fraud involved the CPS and was committed by a senior member of that service - the body responsible for bringing criminals to justice - will have affected and eroded public confidence."

The only mitigating feature in the case, Judge Davis added, was the defendants' previous good character.

Detectives were called in by the CPS in February this year after an internal audit uncovered the bogus claims.

Mahmood was then found to have changed his name by deed poll to open a bank account critical to the fraud.

Commenting after the case, Detective Constable Mark Calvert, who led the inquiry, said: "What we uncovered was a prolonged and systematic fraud by two people who ironically were employed by an organisation which prosecutes those who break the law.

"They naively thought they'd get away with it, but were caught as a result of their own greed."

Financial investigators are still working to try to trace the proceeds of the fraud with a view to returning it to the CPS, the officer added.

The court heard Burrows was authorised to submit invoices for up to £25,000 without recourse to a more senior manager.

Mahmood only worked for the CPS during the last five months of the fraud after being interviewed by Burrows, who did not inform colleagues they were in a relationship.

In a statement, the CPS said: "This fraud was carried out by a member of staff with significant financial authority who abused a position of trust.

"Investigations are being finalised, however an independent external audit provides strong assurances that this was an isolated case.

"Indeed, no further fraudulent activity has been identified.

"Nevertheless, the CPS has strengthened its financial controls and procedures across the organisation in order to prevent, as far as is possible, any fraudulent activity in the future."