ACC fraudsters have ripped off taxpayers by more than $10 million in the past five years. But investigators say catching them and stopping the frauds saved a further $119.6 million.

Figures released to the Herald reveal 138 people have been successfully prosecuted for ACC fraud in the past five years, including "injured" clients who keep working and medical practitioners who bill for too much treatment.

The total amount ranges from $1.2 million to $3.2 million each year, although ACC says the scams would have cost taxpayers much more if the fraudsters had not been caught.

In the 2009-10 financial year, ACC uncovered $1.2 million of false claims. Using actuarial methodology, ACC calculated the true cost would have been $28.1 million if the fraud was undetected and run its expected course.

Many ACC fraudsters are clients who keep working while receiving weekly compensation for lost earnings, lie about an accident, injury or their incapacity, or make false declarations or alter documents.

One of those caught was Timothy Peter Grant Ellwood, considered one of the worst ACC offenders in the past five years.

In September 2008, the truck driver injured his back when bags fell off his truck. He supplied ACC with a medical certificate stating that he was unable to work because of his injury and ACC paid weekly compensation for lost earnings.

Over the next 12 months, Ellwood kept supplying medical certificates to prove he could not work, and ACC kept paying compensation.

However, he never stopped working after his injury and received $25,152 of ACC compensation. The truck driver was convicted of four fraud charges and two ACC charges in the Tauranga District Court in February. He was sentenced to six months' home detention and ordered to repay the money.

"At the end of the day, New Zealanders pay ACC levies to ensure they can get help if they're injured. ACC is committed to ensuring that this money is used for its intended purpose," an ACC spokesman said.

ACC has a dedicated investigation unit to identify and prevent fraud, by acting on tipoffs from the public and analysing data, documents and trends to find any irregularities.

Other ACC client scams include Christchurch woman Vanessa Kennedy, whose husband Grant injured his back landscaping in June 2008. Acting on his behalf, Kennedy told ACC her husband could not work and earned around $75,000 a year.

However, ACC's investigation unit discovered Mr Kennedy was not earning anything and Mrs Kennedy had provided false documents to support her claims.

She was convicted in January and ordered to repay ACC $65,931.80, given 150 hours' community work and put on a six-month community detention curfew between 8pm and 6am.

ACC also investigates medical practitioners who claim for treatment or services not provided, or claim extra time with clients, provide treatment when not needed or forge billing schedules or documents.

Levy payers who misrepresent their levy class to minimise levy rates, or understate or do not declare earnings to minimise levy rates are also investigated.

Auckland-based chiropractor Dean Kenny, a former All Black, admitted billing ACC for 28 blocks of treatment sessions that his clients never received.

Kenny had been providing chiropractic services from two clinics in Orewa and Takapuna.

Kenny pleaded guilty to 28 charges at North Shore District Court in October and was sentenced to 225 hours of community work.

He was also ordered to repay $7956 to ACC.

* Do you know of any ACC fraud? Ring 0508 ACC FRAUD (0508-222-37283).