Image caption Maureen McCleave was fitted with a new type of pacemaker

Medical devices that are unsafe and have not been adequately tested are ending up inside patients' bodies, an investigation has revealed.

The devices include heart pacemakers, rods to correct spines, and artificial knees and hips.

The investigation found implants that had failed in baboons, or were tested only on pigs and dead bodies, were coming onto the market.

The industry says it has transformed millions of lives for the better.

BBC Panorama has been working with the International Consortium of Investigative Journalists and 58 media organisations around the world including The Guardian newspaper and the British Medical Journal.

The investigation found a lax system of regulation in Europe that allows companies to "shop around" dozens of safety organisations until one of them approves their product.

It also found that doctors can be left in the dark about the true risk of treatments they are recommending to their patients.

Maureen 'the good guinea pig'?

Maureen McCleave, 82 from Essex, was the first person in the UK to be fitted with the "Nanostim" pacemaker because of an irregular heartbeat.

Pacemakers are life-saving implants that deliver electrical pulses to the heart to keep them beating regularly.

Traditional ones have leads from a battery to the heart that deliver the electrical pulse, but the cables can break.

The Nanostim was the first leadless pacemaker that sat inside the heart.

Maureen said she was "over the moon" to be the first and felt like a "good guinea pig" when she was implanted with the device at Bart's hospital in London.

"I was so grateful that I'd been chosen, because it sounded too good to be true."

But three years after it was fitted, the battery in Maureen's Nanostim failed and surgeons could not get it out.

She now has a traditional pacemaker keeping her alive. The Nanostim is still sitting inside her heart.

She says: "I don't like the thought I've got a piece of metal or whatever in my heart that's doing nothing and it's just laying there."

Maureen was not alone - a number of batteries failed and parts fell off inside patients.

The pacemaker was withdrawn for safety reasons. At least two people died and ninety events were recorded in which patients were seriously harmed by the device.

The Nanostim heart pacemaker was turned down by safety bodies in Germany because of a lack of evidence. Yet it was approved by the British Standards Institute in the UK.

How big a problem is this?

Not all medical devices are dangerous. Many save lives or dramatically improve quality of life.

But the investigation has found that some devices are failing patients including:

implants that cracked inside people's backs and had failed in baboon tests

birth control implants that caused internal damage and bleeding

misfiring implantable defibrillators

mesh implants for incontinence that caused abdominal pain

The BBC also uncovered a treatment for children with a severely curved spine, or scoliosis, which was allowed on to the market following tests only on pigs and dead bodies.

Yet, due to a lack of transparency and data collection, the scale of any problem across the medical device industry remains a mystery to both patients and doctors.

I have an implant, what should I do?

If you are worried, a panel of experts put together by the International Consortium of Investigative Journalists has put together some advice.

It recommends: "Your first point of call should be the medical team that performed the operation.

"If you cannot go back to them for whatever reason, you should consult your primary care doctor.

"The doctor should be able to refer you to a specialist who is familiar with the device and the surgery you had."

Patients in the UK can also report problems to the regulator.

How is all this allowed to happen?

Europe does not have a governmental body that checks medical devices before they are put onto the market.

Instead a series of companies called notified bodies issue CE marks - the same mark of approval given to devices like toasters and kettles.

There are 58 of them in Europe and approval by one means a product can be used anywhere in the European Economic Area (the EU plus Iceland, Liechtenstein, and Norway).

But if one body says no, a company can shop around and ask another.

But surely you need evidence?

Less than patients might think.

And there is so much secrecy that even surgeons implanting these devices do not always see the evidence upon which a device has been approved for its safety and effectiveness.

The British Standards Institution said it could not discuss the evidence for Nanostim due to "confidentiality requirements".

Even the UK's regulator, the Medicines and Healthcare Products Regulatory Agency, says it is "bound by confidentiality when it comes to some of the actions that we've taken around individual devices".

But the investigation discovered there was only one clinical study before Nanostim was approved for use on the public.

It followed just 33 patients for 90 days.

Image caption Prof Rita Redberg

Prof Rita Redberg, one of the world's leading cardiologists and from the University of California, San Francisco, said: "We're talking about a permanently implanted pacemaker, so I think that's a very tiny study.

"They're supposed to last 10, 20 years. A 90-day follow up is not enough to learn much about the pacemaker."

What does the industry say?

MedTech Europe, the body the represents the medical devices industry, said: "Millions of people have safely benefited from medical devices and can now live healthier, more productive and more independent lives.

"Life is unimaginable today without the hundreds of thousands of medical devices in our hospitals and in our homes."

And it defended the system of notified bodies which were "selected for the expertise, impartiality, transparency and independence of their staff".

Abbott, which manufactured Nanostim, says that many patients have been helped by leadless pacemakers and many more will benefit from this technology in the future.

It said: "In accordance with the European CE Mark approval process, the Nanostim leadless pacing system was approved based on strong performance and safety data.

"In addition, upon CE Mark approval Nanostim was further assessed through a European post market clinical follow-up study."

What is the solution?

The UK's Royal College of Surgeons has called for "drastic regulatory changes".

Prof Derek Alderson, president of the Royal College of Surgeons, said: "All implantable devices should be registered and tracked to monitor efficacy and patient safety in the long-term."

But when the European Union suggested tightening the rules, the industry ran a campaign called "Don't lose the 3".

It referred to the fact that manufacturers can get new products to patients three years quicker in Europe then they can in the United States.

New medical device regulation will come into force in Europe in 2020, but campaigners say the new rules do not go far enough.

German MEP Dagmar Roth Behrendt told Panorama that an intensive lobbying campaign by the industry undermined the proposed reforms.

"It's a success for them and a failure for the European parliament and for European patients, I have no doubt about it.

"It is like an open wound for me, that we could not do more for European patients and for the safety of European patients hurts."