The French company facing a criminal investigation over the content and safety of its breast implants were warned of their dangers at least seven years ago.

A Sky News investigation also found the firm, Poly Implants Protheses (PIP), was accused by its insurers a year later of deliberately concealing complaints from regulators, surgeons and clinics.

A report by a consultant plastic surgeon in Los Angeles in 2005 warned that PIP implants were three-and-a-half times more likely to rupture than a test group.

Dr. Grant Stevens compared 500 PIP implants with 500 implants manufactured by Mentor Siltex. After four years, 15 percent of the PIP implants had ruptured compared to just four percent of those made by the other brand. Stevens claims that at the time, PIP asked him not to report his studies.

Sky News also obtained a copy of a letter PIP received from its insurers in 2006, accusing it of failing to notify them or French regulators of incidents that would necessitate the implants' removal, despite it being compulsory to do so.

"We are observing there are over 4,000 claims. PIP received 466 claims before 1999 and 1,783 claims between 2000 and 2002. Until 2005 our company was notified of only four events," the letter said.

"Your company has therefore systematically concealed for many years the claims received from surgeons or clinics in relation to incidents and removals of your prosthesis," it added. "We hold that PIP, by a deliberate, willful and financially-rewarding violation of the regulations, prevented the authorities conducting an inquiry to try [to] stop the incidents."

The letter was one of several warnings about PIP dating over a decade.

In March 2000, US regulators found 11 deviations from "good manufacturing practices" at the PIP factory in France.

In February 2009, the UK regulatory authority was warned of a number of medical claims against the company, which is based in La Seyne-sur-Mer near Toulon in southeastern France.

The French government now advises patients who were fitted with PIP implants to have them removed, and has even offered to pay for the surgery, provided the original procedure was for reconstructive and not cosmetic reasons.

It has also been discovered that PIP made products for men including prosthetic testicles.

Employees of the now-closed PIP told the Le Parisien Daily that the firm manufactured testicle, chest and buttocks implants for men, The Independent reported Thursday.

The fake testicles -- used by patients who have undergone surgery for testicular cancer -- were shipped worldwide, but the number of men who had them fitted was not known.

A former PIP employee told Le Parisien that the male buttocks and chest implants contained the same gel as the breast implants at the center of the global health scare.

"For aesthetic reasons some of our clients, especially those in South America, ordered them, and in that case the gel used to make them was the suspect gel," the ex-employee said.

It was not immediately clear if the sub-standard silicone was also used in the testicular implants.

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