The number of British women who have been given faulty breast implants is about 7,000 higher than previously thought, the UK government announced on Thursday.
French authorities had advised that implants made by Poly Implant Prothese (PIP) — using industrial-grade silicone designed for use in mattresses — were only sold after 2001.
But an investigation by the Medicines and Healthcare products Regulatory Agency, the UK regulator, found that PIP devices made before this date may also have contained the gel.
The additional cases mean a total of 47,000 British women are now believed to have been given faulty implants made by the French company.
Women who have PIP implants, or those who do not know the make of their implants, are being urged to visit their GP for advice. Most cosmetic surgeons are now offering to remove the faulty implants free of charge but several large companies are refusing.
The NHS will not charge to remove any PIP implants that have ruptured, if the original clinic refuses to do so, health officials said.
Andrew Lansley, the health secretary, said: "I want to reassure those affected by the news today that they will be provided with all the help they need from the NHS.
"We are still working to get private clinics to live up to their responsibilities and look after their patients.
"Our commitment is to ensure support for all women from the NHS if needed; we will continue to press for the same standard of care or redress from private providers."
To date, the removal programme has cost the NHS at least £5,00,000 with 4,534 women seeking help from the health service. Most breast implants need to be replaced after 10 to 15 years so a proportion of the faulty implants may already have been removed as part of routine replacement operations.
The Medicines and Healthcare products Regulatory Agency has advised that there is no need to replace the PIP implants unless they have ruptured, however most women are so concerned they are asking for them to be taken out.
This week one woman disclosed that her credit card company had refunded the cost of her breast implant surgery under the Faulty Goods Act.
The Department of Health has ordered two reviews, one looking specifically at how the PIP implants were approved and their safety. The second will examine the regulation of cosmetic surgery more widely.
In December the French authorities recommended that all women who had PIP implants should have them removed and that the French government would pay for the surgery.
Experts in Britain have not found any link between the faulty implants and an increased risk of cancer, and it is not clear whether the PIP implants are more likely to rupture than other implants
But private clinics have been told they have a moral duty to remove PIP implants in cases where women have expressed concerns.
The owner of the company is facing charges of "involuntary injury".
Jean-Claude Mas, 72, had been freed on bail of €1,00,000 (pounds 83,000).
Mas has been under investigation since he disclosed in a police interview last year that PIP ordered employees to hide the unauthorised silicone when inspectors visited its factory. Up to 4,00,000 women in 65 countries are believed to have been given the implants.