Nearly 50,000 British patients with all-metal artificial hips will need annual tests for the life of their implants to monitor for problems, including exposure to toxic metals, Britain's medical regulator said on Tuesday.

Patients with large-head implants should have blood tests to check for metal ions and magnetic resonance imaging scans (MRI) if they have raised metal levels or show adverse symptoms, the Medicines and Healthcare Products Regulatory Agency (MHRA) said.

It issued the new clinical guidelines to doctors after reports of swelling and tissue damage in some patients, and high failure rates with certain devices.

The regulator said around 49,000 patients out of 65,000 with all-metal hips fell into the high-risk category.

The move will fuel controversy about the regulation of medical devices in Europe in the wake of a scandal over France's Poly Implant Prothese (PIP) breast implants. Critics argue European oversight is too lax to spot substandard products.

The MHRA update comes on the same day as an investigation by the British Medical Journal into all-metal artificial hips, which warned that the problem may affect more people than the breast implant scandal.

Metal-on-metal hips were developed to be more durable than traditional implants, which combine a metal or ceramic ball with a plastic socket.

But patients receiving some all-metal hips turned out to be more likely to need repeat surgery than those who got implants made of other materials. They also produce debris that can release chromium and cobalt ions into the blood, causing health problems and potential damage to chromosomes.

We shouldn't be in this position where we don't know and there's so much uncertainty. The stability of a compound should have been ascertained before it was used widely in people, said Nick Freemantle, Professor of Clinical Epidemiology and Biostatistics at University College London.

Under the new MHRA guidance, doctors are being advised to consider removing and replacing implants if patients have abnormal MRI scans or if metal ion levels in the blood reach worrying levels.

J&J RECALL

In 2010, Johnson & Johnson issued a massive recall of its DePuy ASR all-metal hip implant system that failed at a higher-than-expected rate, and last month the company took a charge of more than $3 billion largely related to the recall.

The latest advice for life-long checks in the case of all-metal implants with a head diameter greater than 36 millimetres (mm) updates previous guidance from April 2010 that patients only needed to be monitored for five years after their operation.

The new guidance does not affect all-metal hips under 36 mm in diameter or resurfacing systems with no stem sticking into the bone, such as Smith & Nephew's Birmingham Hip Resurfacing joints.

Following the controversy over metal-on-metal hips, their rate of use has fallen markedly in Britain to around 5 percent of hip replacement operations in 2010 from around 15 percent four years earlier, a trend the MHRA said it welcomed.

For a small group of patients this implant is still good news and we don't want to take them completely off the market, Susan Ludgate, the agency's clinical director, told reporters.

But the use of these implants has come crashing down over the last few years and that's where we want it to be.

Other companies that make metal-on-metal hip implants include Zimmer, Stryker, Corin, Biomet, Implacast, Wright Medical, Joint Replacement Instrumentation and Finsbury/MatOrtho, according to the MHRA.

(Reporting by Ben Hirschler; editing by Kate Kelland and Erica Billingham)