The scale of the breast implant scandal involving faulty silicone devices given to more than 40,000 British women cannot be determined because no one knows the true failure rate of the devices, leading surgeons admitted yesterday.

The lack of regulation of cosmetic surgery clinics means no reliable records of the rupture rate for breast implants exist and risks to patients cannot be assessed, experts said.

The disclosure poses a challenge for the government review of the faulty implants manufactured by the French firm Poly Implant Prothèse (PIP). The Medicines and Healthcare products Regulatory Agency, which approves the devices in the UK, said the failure rate was less than 1 per cent but in France the government has estimated the failure rate at 5 per cent.

One major UK cosmetic clinic chain, Transform, has told the Department of Health its rupture rate for the PIP implants was 7 per cent, over seven times higher than the official figure.

The British Association of Aesthetic Plastic Surgeons demanded yesterday that every breast implant be recorded on a national register and manufacturers made subject to random checks. Nigel Mercer, former president of the association, said: "When the MHRA quoted a 1 per cent failure rate we asked ourselves, where did they get that from?"