Shell has been officially censured for breaking safety rules 25 times in the last six years and has one of the worst safety records of the major oil companies in the UK, an investigation by the Sunday Herald has revealed.

The British oil multinational has been prosecuted, fined and formally reprimanded for repeatedly failing to maintain pipelines and other vital equipment in the North Sea, for failing to report a dangerous incident, and for failing to protect workers from hazardous chemicals.

The revelations, from records held by the Government’s Health and Safety Executive (HSE), have led to renewed criticism of Shell in the wake of last week’s oil leak from a pipeline to the Gannet Alpha platform 112 miles east of Aberdeen. The company has been slammed for failing to be open about the leak, which it claimed to have sealed on Friday.

Now, critics have lambasted Shell for being a “serial offender” that refuses to learn from its mistakes. And they warn that the regulatory regime meant to ensure the safety of the North Sea oil industry is no longer fit for purpose.

“This shocking history of warnings, violations and prosecutions could suggest a company that is cutting corners on essential maintenance and skimping on safety,” said Dr Richard Dixon, director of the environmental group, WWF Scotland.

“With such a lamentable performance, something like the Gannet Alpha spill was almost bound to happen. The question now is what other knackered bits of kit are about to give out.”

Dixon called for Shell’s North Sea operations to be restricted until a full and independent audit of all its facilities had been carried out. “Shell’s poor regard for safety and their terrible communications over the last 10 days should be ringing major alarm bells with the UK Department of Energy and Climate Change and the HSE,” he argued.

The HSE maintains online databases of all the prosecutions, prohibition orders and improvement notices against UK companies for breaching health and safety regulations. An analysis of those involving oil companies shows that Shell is among the top offenders.

Since 2005, Shell has been prosecuted four times: for an explosion at Bacton gas terminal near Norwich; an accident at Ellesmere Port in Cheshire; a collision at the Mossmoran gas plant in Fife; and a fatality on the Clipper rig in the North Sea. The company has been forced to pay out nearly £1 million in fines and legal costs.

No other major oil company has faced as many prosecutions in the last six years. According to the HSE, Talisman has been prosecuted twice, while BP, Total, Amec and Nexen have each been prosecuted once (see table).

In addition, Shell has been served with 21 prohibition and improvement notices by HSE safety inspectors since 2005. The company has twice been told it was guilty of a “failure to implement a suitably resourced maintenance regime” on the Clipper rig, once in 2006 and again in 2007.

“This has lead to excessive backlog of maintenance activities for safety-critical equipment and non-safety-critical equipment, leading to poor working order and repair of equipment,” said the HSE.

In October 2009, Shell was served an urgent prohibition notice to remedy dangers on the Brent Charlie platform. According to HSE, there was “a risk of serious personal injury because there is no effective means of safely removing toxic and flammable gas” from below a floor.

In April 2007, Shell was accused by HSE of failing to report “by the quickest practicable means that there was a dangerous occurrence” on the Dunlin Alpha rig. There have also been maintenance failures on Brent Bravo and Leman Alpha, as well as problems controlling exposure to asbestos on Leman Charlie and another toxic chemical on Dunlin Alpha (see table below).

Only one oil company has received more enforcement notices than Shell. That is the Danish corporation, Maersk, which has been served 33 prohibition and improvement notices by HSE since 2005. But it hasn’t been prosecuted.

Other evidence previously released under freedom of information law shows that Shell rigs have one of the worst records for oil spills in the North Sea over the last two years. There were leaks from seven of the company’s platforms in 2009 and 2010.

The most spills were from the Brent Charlie rig, which suffered seven leaks in the two years. The biggest was in April last year when an escape of four tonnes of gas triggered a production shutdown.

Shell’s poor track record prompted experts to question whether the current regulatory regime is working. The company’s performance was “deeply worrying” in an industry which suffered “serious and often potentially catastrophic shortcomings,” warned Professor Andrew Watterson, head of the occupational and environmental health research group at the University of Stirling.

He pointed out that ensuring health and safety for oil workers should help reduce pollution. “But this will not happen if companies can escape the consequences of poor performance and offset much of the human, environmental and economic damage they do onto injured workers and wildlife,” he argued.

According to Watterson, oil and gas spills in the offshore industry as a whole rose from 65 in 2008-09 to 85 in 2009-10. At the same time, major injuries rose sharply from 106 to 188 per 100,000 workers.

“The number of HSE offshore inspectors in the same years fell from 98 to 90,” he said. “These are not figures that inspire confidence either in the oil industry or the increasingly run-down regulators.”

The HSE, however, insisted it had an established record of holding oil companies to account. The offshore industry was obliged to adopt high standards, which were independently checked, it said.

“Although we are confident that we have one of the most robust safety regimes in the world, we are not complacent,” said an HSE spokesman. “The penalties imposed for breaches of offshore regulations are a matter for the courts.”

He added: “HSE’s enforcement notices database is not designed to be read as a safety league table. Counting the number of enforcement notices does not take account, for example, of the number of installations a company may operate.”

Shell stressed that its “prime focus” was a commitment to ensur- ing the safety of staff and infrastruc- ture. “We constantly inspect, monitor and review all our assets,” said a company spokeswoman.

“We work closely with regulators and have invested over $1 billion in recent years to upgrade facilities across the North Sea.”

But that is not going to comfort environmentalists. “Shell appears to have one of the poorest safety records of the major oil companies,” said Stan Blackley, the chief executive of Friends of the Earth Scotland.

“This doesn’t really surprise us, but it’s depressing all the same. Already some environmental and human rights groups claim Shell has a reputation for poor practice, complacency and misinformation.”

Blackley said Shell was fiercely criticised for pollution and human rights abuses in the Niger Delta. “Fining Shell is not going to make it change its ways,” he warned.

“The executives running the business need to be held accountable for any failings or wrongdoings and, if found guilty of any breach of the law, prosecuted to the full extent of the law.”