More than one in three NHS organisations and almost a quarter of private clinics that provide breast implant surgery may be putting women at risk by not adding their data to a national registry which keeps track of the safety of implants.
The register was recommended as a result of the breast implant scandal which saw some women fitted with faulty French implants.
It records the details of every person who has breast implant surgery in case of a product recall or another safety concern.
But NHS Digital, which manages the register, said that 39% of NHS providers and 24% of independent providers who offer breast implant surgery are yet to register patient details.
The Breast and Cosmetic Implant Registry was launched in October 2016.
PIP (Poly Implant Prostheses) implants were withdrawn from the UK market in 2010 after it was found they had been filled with non-medical grade silicone intended for use in mattresses.
Estimates suggest that as many as 47,000 women in the UK had been fitted with the implants, but the exact figure is not known.
A UK government-ordered report in June 2012 found the implants were made from an unauthorised silicone filler and ruptured at twice the rate of other implants.
It was recommended that a national registry was created so that faulty implants could be efficiently tracked if products turn out to be faulty.
NHS Digital has now asked women undergoing such treatment to ensure their surgeon has registered their details - which can only be added provided they have given consent.
Tom Denwood, executive director of data, insights and statistics at NHS Digital, said: "The development of the Breast and Cosmetic Implant Registry marked a major step forward in improving patient safety for those undergoing breast implant surgery.
"Now we are encouraging patients to ask their surgeon to submit their data to the registry and we hope this will lead to an increase in contributions.
"The more information that is contained within this important tool, the more it will benefit patients."
Health Minister Jackie Doyle-Price added: "It's vital that patients undergoing breast implant procedures encourage their surgeons to record their details on the registry to safeguard their health.
"The confidential record allows patients to be contacted if their safety is at risk and will hopefully give people the confidence they need when making decisions on surgery."
Alison Lattimer, a patient representative on the Breast and Cosmetic Implant Registry Steering Group, added: "As someone who has undergone breast reconstruction surgery, I can understand how worrying it can be if patient safety issues arise, sometimes years later.
"We want more patients to be aware that this registry exists and to ask their surgeons about having their details included.
"The registry also provides patients with confidence and assurance when making decisions about implant surgery that they will be followed up if there are problems with the implants in the future.