Radioactive materials have gone missing from businesses, hospitals and even schools more than 30 times over the last decade, a freedom of information request to the UK’s health and safety authorities has revealed.

Nuclear experts have warned that some of the lost material could be used by terrorists and said there should be a crackdown by the regulators to ensure such “carelessness” is brought to a speedy halt.

Among the big names that have lost potentially dangerous materials are Rolls-Royce at a site in Derby, the Sellafield nuclear plant in Cumbria and the Royal Free hospital in London. Some organisations have been prosecuted but others have got away with little more than a warning notice, papers released by the Health and Safety Executive (HSE) reveal.

Missing items include a 13kg ball of depleted uranium from the Sheffield Forgemasters steel operation in 2008, plus small pellets of extremely radioactive ytterbium-169 from Rolls-Royce Marine Operations.

The Royal Free hospital lost caesium-137 – used in cancer treatment – which a report into the incident accepted had “the potential to cause significant radiation injuries to anyone handling [it] directly or being in the proximity for a short period of time.”

In another case, at the site of the former atomic energy research station at Harwell near Oxford, cobalt-60 was “found in a tube store under a machine during clearance,” according to the HSE.

The oil services firm Schlumberger also “temporarily lost” caesium-137 radioactive materials on a North Sea platform, while Southampton General hospital could not locate an “unsealed source” of iodine-131 in February last year.

John Large, an internationally renowned consultant to the nuclear industry, said it was disturbing that losses of the magnitude detailed were happening so frequently.

“The unacceptable frequency and seriousness of these losses, some with the potential for severe radiological consequences, reflect poorly on the licensees and the HSE regulator, whose duty is to ensure that the licensee is a fit and competent organisation to safeguard such radiological hazardous materials and substances. I cannot understand why it is not considered to be in the public interest to vigorously prosecute all such offenders.

“Clearly these organisations have been careless and wanting in their duty to safeguard and secure these radioactive substances, some of which remain extremely radiologically hazardous for many years – such slack security raises deep concerns about the accessibility of these substances to terrorists and others of malevolent intent.”

The HSE said it always considered all enforcement action against those involved, up to and including prosecution, but its final decision rested on issues including the likelihood of securing a conviction and the public interest. “Prosecutions have been undertaken successfully by HSE in the case of Schlumberger and the Royal Free hospital,” it said in a statement.

By contrast, the universities of York and Warwick received “written advice” and an “improvement notice” respectively over the loss of radioactive materials used for demonstrations in their science departments. Loreto high school in Manchester is being investigated by the HSE over the loss of an americium-241 radioactive source and four small mineral samples.

In February of this year the Sellafield nuclear plant pleaded guilty at Workington magistrates court to sending several bags of radioactive waste to the wrong facility.

The company was prosecuted by the Environment Agency and the Office for Nuclear Regulation after four bags of mixed general waste, such as plastic, paper, tissues, clothing, wood and metal, from normal operations in controlled areas of the site were sent to Lillyhall landfill site in Workington. The bags should have been sent to the Low Level Waste Repository at Drigg, Cumbria, – a specialist facility which treats and stores low-level radioactive waste consignments.

Large, who led the nuclear risk assessment team for the raising of the damaged Russian nuclear submarine Kursk in 2001, said in a number of cases publicised through the FoI disclosure people seemed to have been potentially put in danger. “The licensed use of such radioactive sources requires the licensee to be a fit person and demonstrate competence and each of the sources is accompanied by ‘cradle to grave’ documentation that requires a prearranged and managed storage/disposal route – these safeguards have clearly failed and the workforce and, indeed, members of the public may have been placed at radiological risk.”

He added: “Some of these lost radioactive sources are very persistent, for example the Royal Free hospital’s lost caesium-137 has a radioactive decay half-life of around 30 years, so it remains radio-toxic for at least 10 half-lives or about 300 years, and the unsealed source of iodine-131 lost by Southampton hospital is extremely volatile, easily breathed in and reconcentrated by the thyroid gland, presenting a cancer risk, and certainly not amenable to release into the atmosphere of a public place such as a hospital.”