* The affected medicines contain azido-tetrazole, health chiefs have revealed * Government officials warned the substance may increase the risk of cancer * Scientists have also dubbed substance the world's most explosive chemical

Health chiefs today recalled dozens of batches of blood pressure pills because they were found to contain an explosive chemical.

Pharmacies stocking the affected drugs — several different types of irbesartan and losartan — were told to pull them after the cancer-causing impurity was detected.

The Medicines and Healthcare products Regulatory Agency, which polices the safety of drugs used in Britain, said the affected batches contained azido-tetrazole.

Government officials warned the substance – considered by some to be the world's most explosive chemical – may increase the risk of cancer.

But the MHRA insisted the measure was merely a precaution and there was no proof it has caused any harm to patients.

It urged Brits told not to stop taking the drugs without consulting their GP because suddenly stopping can be risky.

Some of the contaminated pills have been on the market for nearly two years, it was also revealed.

It is the latest in a line of drug recalls of sartan-type medicines, which may have been exposed to cancer-causing chemicals in factories in China and India.

Irbesartan and losartan are prescribed to millions of Britons with high blood pressure every year.

There is also no evidence any of the pills have exploded.

The MHRA said the move only applied to pharmacies and wholesalers stocking the 31 batches supplied by Bristol Laboratories Limited, Brown & Burk UK Limited and Teva UK Limited, some of which were first distributed in September 2019.

Other blood pressure pills containing losartan and irbesartan are still available.

Dr June Raine, chief executive of the MHRA, said: 'Patient safety is our watchword.

'We're recalling batches of certain sartan-containing as precautionary measure while we continue our investigation.

'It's important that healthcare professionals check their stock to quarantine and return these batches.

'If you've been taking one of the affected products, speak with your doctor or pharmacist before stopping any treatment – they can address any concerns and can advise you on the best course of action.'

Cambridge University chemical scientist Dr Ljiljana Fruk described azido-tetrazole as the the world's 'most explosive chemical' in 2019.

Speaking on the The Naked Scientists radio show, she said: 'So the most explosive chemical was made in 2011 in the lab.

'[It] Never went out of the lab, it was made in a special chamber and it's called azido-tetrazole.

'So that's a molecule that has 14 nitrogens in its own structure, and because of these constrained nitrogen bonds it's very explosive.'

Dr Fruk, from Cambridge's Department of Chemical Engineering and Biotechnology, added: 'Some scientists said that this molecule could explode even if you look at it, because you know it really reacts on a tiniest amount of pressure.'

Officials have yet to explain how the latest impurity may have occurred.

But they are often caused by contamination in factories or brought on during the manufacturing or storage process.

Exposure to light, temperatures or even reactions with the container that holds the drug can trigger chemical changes.

Overall, more than two-thirds of all active drug ingredients originate in China and India, industry experts estimate, with China accounting for the lion's share.

NHS figures reveal more than 2million prescriptions for drugs containing irbesartan were dished out in England in 2017.

It comes after a similar recall saw thousands of blood pressure pills pulled from pharmacy shelves in January after carcinogenic ingredients were found in them.

Four types of irbesartan hydrochlorothiazide pills were contaminated with N nitrosodiethylamine (NDEA), a chemical once used in rocket fuel.

Around 165,000 people are prescribed irbesartan hydrochlorothiazide every year for hypertension – the medical term for high blood pressure.

US drug regulators, the FDA, announced in November that Indian pharmaceutical firm, Aurobindo Pharma Ltd, had recalled 22 products containing irbesartan amid fears they also had the NDEA impurity.

EU officials then announced they were 'considering' whether to recall medicines containing the Indian firm's irbesartan as a precaution. It was then suspended from supplying the chemical to other firms in Europe.

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