Tests on breast implants manufactured by a French company have found no evidence of cancer-causing substances, experts said.

The UK Medicines and Healthcare products Regulatory Agency (MHRA) said it had received "encouraging results" from tests on silicone gel breast implants manufactured by the company Poly Implant Prosthese (PIP).

Fears had been raised that the implants were filled with an unapproved gel and were missing protective barriers.

Some 50,000 British women are thought to have had the implants.

The MHRA said it had found no evidence of substances which had potential for cancer or chemical toxicity, though more extensive tests were still being carried out in France.

The French company PIP has gone into administration.

MHRA director of devices clinical, Dr Susanne Ludgate, said: "It's reassuring that our test results have shown no evidence of any associated risks with the filler material. We are, however, waiting for the results of the French tests which are more extensive and include mechanical testing of the implant shell because there may be a suggestion of an increased rupture rate compared with other breast implants.

"We will update clinicians and women once these test results are available and provide further advice on patient management as necessary."

The British Association of Aesthetic Plastic Surgeons (BAAPS), welcomed the news but said any ruptured implants, of any kind, would still need removing.

BAAPS president Nigel Mercer said: "We would like to praise the MHRA for their proactive response in conducting safety tests and are delighted that there is little risk to patients from the gel. Hopefully this will reduce the anxiety of patients whilst further studies are expected from France. Our advice remains that women with suspected rupture contact their surgeon and undergo an ultrasound and removal, as they should with any ruptured implant."