Up to £5.7 billion a year could be lost by the NHS to fraud by patients and staff, a new report has claimed.
A review led by Jim Gee, a former director of NHS Counter Fraud Services, suggested fraud was taking place across areas such as general practice, dentistry, prescriptions and payroll.
Among examples of fraud cited in the report were GPs creating "ghost patients", dentists claiming for more work than was carried out and pharmacists failing to declare prescription charges which have been paid.
Mr Gee and co-author Professor Mark Button, director of the Centre for Counter Fraud Studies at Portsmouth University, said they hoped the research "focusses attention" on the issue, adding the NHS needed to improve how it measured fraud losses.
The authors of the report, published by PKF Littlejohn accountants, said: "Fraud has negative consequences in all sectors, but in healthcare the impact of fraud is even more pernicious. Quite simply it has a direct, negative impact on human life as the quality, quantity and speed of patient care is diminished."
The are with the highest estimated losses to fraud and error was payroll, at between £555 million and £1.49 billion - where scams included false allowance claims.
Procurement scams, such as under-providing goods and services, was estimated to cost between £1 billion and £1.27 billion, while between £304 million was lost to fraud by patients through false claims for free prescriptions, dental care and optical services.
The overall level of fraud, based on an analysis of loss measurement data from the UK and around the world, was said to cost between £3.7 billion and 5.7 billion of the £110 billion NHS budget in 2013-2014.
Mr Gee told the BBC: "There is a vast, honest majority who find fraud against the NHS to be completely unacceptable. However, there is also a dishonest minority who can cause significant financial damage.
"The best way of stopping this is not to wait for fraud to happen and then act after losses have been incurred, but to proactively deter and prevent them. Fraud is a cost to be measured, managed and minimised like any other."