Oil giant Shell is to launch a bid to leave the 10 vast concrete legs of three oil rigs standing in the North Sea for up to 500 years after the platforms have been decommissioned.

The company’s proposals also include the controversial suggestion that oil mixed with sediment in 42 out of 64 concrete storage cells – each up to 20 metres in diameter and 60 metres high, taller than Nelson’s Column – should remain on the sea bed.

The decommissioning of the historic Brent field, created during the 1970s boom, represents the Government’s first big decision on what will happen to the main North Sea installations as they stop producing oil.

Environmentalists said they accepted the principle that structures could be left in the sea if it was too dangerous to remove them, but stressed Shell had a “legal, as well as moral, obligation to clean-up their mess” and remove the oily sediment.

The fishing industry said they would prefer "a return to a clean seabed" but appreciated the problems in removing the structures.

Shell’s plan will detail how the company wants to decommission the four Brent oil rigs, three of which rest on concrete legs. Each of those rigs, Brent Bravo, Charlie and Delta, weighs the same as the Empire State Building and is about the same height as the Eiffel Tower.

Trump signs executive orders to advance oil pipelines

Under the plan, the platforms would be removed but the concrete legs would remain sticking up out of the sea and the concrete cells would be sealed with any oily sediment left inside.

Duncan Manning, the business opportunity manager for the Brent Decommissioning project, told The Independent that their modelling of what would happen over the coming centuries suggested the oil would have a “very small” effect on the environment when eventually the storage cells collapse.

“This sediment is going to remain encased or entombed in these structures for hundreds of years,” he said. “The legs will remain in place for 150 to 250 years. They will eventually degrade at sea level and then slowly crumble down.

“If they are pushed over in a storm, then they fall on the cells beneath. We got engineers to look at that.

“While we anticipate because of the weight of the legs, the tops of the cells will crumble, the base of the cell will remain effectively as a bund to hold the sediment in place. The roof of the cells collapses into the cell itself. At that point, you will get some exposure [of the sediment] into the marine environment.”

World news in pictures Show all 50 1 /50 World news in pictures World news in pictures 14 September 2020 Japan's Prime Minister Shinzo Abe, Chief Cabinet Secretary Yoshihide Suga, former Defense Minister Shigeru Ishiba and former Foreign Minister Fumio Kishida celebrate after Suga was elected as new head of the ruling party at the Liberal Democratic Party's leadership election in Tokyo Reuters World news in pictures 13 September 2020 A man stands behind a burning barricade during the fifth straight day of protests against police brutality in Bogota AFP via Getty World news in pictures 12 September 2020 Police officers block and detain protesters during an opposition rally to protest the official presidential election results in Minsk, Belarus. Daily protests calling for the authoritarian president's resignation are now in their second month AP World news in pictures 11 September 2020 Members of 'Omnium Cultural' celebrate the 20th 'Festa per la llibertat' ('Fiesta for the freedom') to mark the Day of Catalonia in Barcelona. Omnion Cultural fights for the independence of Catalonia EPA World news in pictures 10 September 2020 The Moria refugee camp, two days after Greece's biggest migrant camp, was destroyed by fire. Thousands of asylum seekers on the island of Lesbos are now homeless AFP via Getty World news in pictures 9 September 2020 Pope Francis takes off his face mask as he arrives by car to hold a limited public audience at the San Damaso courtyard in The Vatican AFP via Getty World news in pictures 8 September 2020 A home is engulfed in flames during the "Creek Fire" in the Tollhouse area of California AFP via Getty World news in pictures 7 September 2020 A couple take photos along a sea wall of the waves brought by Typhoon Haishen in the eastern port city of Sokcho AFP via Getty World news in pictures 6 September 2020 Novak Djokovic and a tournament official tends to a linesperson who was struck with a ball by Djokovic during his match against Pablo Carreno Busta at the US Open USA Today Sports/Reuters World news in pictures 5 September 2020 Protesters confront police at the Shrine of Remembrance in Melbourne, Australia, during an anti-lockdown rally AFP via Getty World news in pictures 4 September 2020 A woman looks on from a rooftop as rescue workers dig through the rubble of a damaged building in Beirut. A search began for possible survivors after a scanner detected a pulse one month after the mega-blast at the adjacent port AFP via Getty World news in pictures 3 September 2020 A full moon next to the Virgen del Panecillo statue in Quito, Ecuador EPA World news in pictures 2 September 2020 A Palestinian woman reacts as Israeli forces demolish her animal shed near Hebron in the Israeli-occupied West Bank Reuters World news in pictures 1 September 2020 Students protest against presidential elections results in Minsk TUT.BY/AFP via Getty World news in pictures 31 August 2020 The pack rides during the 3rd stage of the Tour de France between Nice and Sisteron AFP via Getty World news in pictures 30 August 2020 Law enforcement officers block a street during a rally of opposition supporters protesting against presidential election results in Minsk, Belarus Reuters World news in pictures 29 August 2020 A woman holding a placard reading "Stop Censorship - Yes to the Freedom of Expression" shouts in a megaphone during a protest against the mandatory wearing of face masks in Paris. Masks, which were already compulsory on public transport, in enclosed public spaces, and outdoors in Paris in certain high-congestion areas around tourist sites, were made mandatory outdoors citywide on August 28 to fight the rising coronavirus infections AFP via Getty World news in pictures 28 August 2020 Japanese Prime Minister Shinzo Abe bows to the national flag at the start of a press conference at the prime minister official residence in Tokyo. Abe announced he will resign over health problems, in a bombshell development that kicks off a leadership contest in the world's third-largest economy AFP via Getty World news in pictures 27 August 2020 Residents take cover behind a tree trunk from rubber bullets fired by South African Police Service (SAPS) in Eldorado Park, near Johannesburg, during a protest by community members after a 16-year old boy was reported dead AFP via Getty World news in pictures 26 August 2020 People scatter rose petals on a statue of Mother Teresa marking her 110th birth anniversary in Ahmedabad AFP via Getty World news in pictures 25 August 2020 An aerial view shows beach-goers standing on salt formations in the Dead Sea near Ein Bokeq, Israel Reuters World news in pictures 24 August 2020 Health workers use a fingertip pulse oximeter and check the body temperature of a fisherwoman inside the Dharavi slum during a door-to-door Covid-19 coronavirus screening in Mumbai AFP via Getty World news in pictures 23 August 2020 People carry an idol of the Hindu god Ganesh, the deity of prosperity, to immerse it off the coast of the Arabian sea during the Ganesh Chaturthi festival in Mumbai, India Reuters World news in pictures 22 August 2020 Firefighters watch as flames from the LNU Lightning Complex fires approach a home in Napa County, California AP World news in pictures 21 August 2020 Members of the Israeli security forces arrest a Palestinian demonstrator during a rally to protest against Israel's plan to annex parts of the occupied West Bank AFP via Getty World news in pictures 20 August 2020 A man pushes his bicycle through a deserted road after prohibitory orders were imposed by district officials for a week to contain the spread of the Covid-19 in Kathmandu AFP via Getty World news in pictures 19 August 2020 A car burns while parked at a residence in Vacaville, California. Dozens of fires are burning out of control throughout Northern California as fire resources are spread thin AFP via Getty World news in pictures 18 August 2020 Students use their mobile phones as flashlights at an anti-government rally at Mahidol University in Nakhon Pathom. Thailand has seen near-daily protests in recent weeks by students demanding the resignation of Prime Minister Prayut Chan-O-Cha AFP via Getty World news in pictures 17 August 2020 Members of the Kayapo tribe block the BR163 highway during a protest outside Novo Progresso in Para state, Brazil. Indigenous protesters blocked a major transamazonian highway to protest against the lack of governmental support during the COVID-19 novel coronavirus pandemic and illegal deforestation in and around their territories AFP via Getty World news in pictures 16 August 2020 Lightning forks over the San Francisco-Oakland Bay Bridge as a storm passes over Oakland AP World news in pictures 15 August 2020 Belarus opposition supporters gather near the Pushkinskaya metro station where Alexander Taraikovsky, a 34-year-old protester died on August 10, during their protest rally in central Minsk AFP via Getty World news in pictures 14 August 2020 AlphaTauri's driver Daniil Kvyat takes part in the second practice session at the Circuit de Catalunya in Montmelo near Barcelona ahead of the Spanish F1 Grand Prix AFP via Getty World news in pictures 13 August 2020 Soldiers of the Brazilian Armed Forces during a disinfection of the Christ The Redeemer statue at the Corcovado mountain prior to the opening of the touristic attraction in Rio AFP via Getty World news in pictures 12 August 2020 Young elephant bulls tussle playfully on World Elephant Day at the Amboseli National Park in Kenya AFP via Getty World news in pictures 11 August 2020 French Prime Minister Jean Castex is helped by a member of staff to put a protective suit on prior to his visit at the CHU hospital in Montpellier AFP via Getty World news in pictures 10 August 2020 Locals harvest their potatoes as Mount Sinabung spews volcanic ash in Karo, North Sumatra province, Indonesia Antara Foto/Reuters World news in pictures 9 August 2020 Doves fly over the Peace Statue at Nagasaki Peace Park during the memorial ceremony held for the 75th anniversary of the atomic bombing EPA World news in pictures 8 August 2020 Anti-government protesters try to remove concrete wall that installed by security forces to prevent protesters reaching the Parliament square, during a protest against the political elites and the government after this week's deadly explosion in Beirut AP World news in pictures 7 August 2020 A protester throws a stone towards Israeli forces in the village of Turmus Aya, north of Ramallah in the occupied West Bank, following a march by Palestinians against the building of Israeli settlements AFP via Getty World news in pictures 6 August 2020 A woman yells as soldiers block a road for French President Emmanuel Macron's visit the Gemmayzeh neighborhood. The area in Beirut suffered extensive damage from the explosion at the seaport AP World news in pictures 5 August 2020 Damage at the site of Tuesday's blast in Beirut's port area, Lebanon Reuters World news in pictures 4 August 2020 A large explosion in the Lebanese capital Beirut. The blast, which rattled entire buildings and broke glass, was felt in several parts of the city AFP via Getty World news in pictures 3 August 2020 A general view shows the new road bridge in Genoa, Italy ahead of its official inauguration, after it was rebuilt following its collapse on August 14, 2018 which killed 43 people Reuters World news in pictures 2 August 2020 Empty stall spaces are seen hours before a citywide curfew is introduced in Melbourne, Australia EPA World news in pictures 1 August 2020 People take part in a demonstration by the initiative "Querdenken-711" with the slogan "the end of the pandemic - the day of freedom" to protest against the current measurements to curb the spread of COVID-19 in Berlin, Germany AFP via Getty World news in pictures 31 July 2020 Pilgrims circumambulating around the Kaaba, the holiest shrine in the Grand mosque in Mecca. Muslim pilgrims converged today on Saudi Arabia's Mount Arafat for the climax of this year's hajj, the smallest in modern times and a sharp contrast to the massive crowds of previous years Saudi Ministry of Media/AFP World news in pictures 30 July 2020 The Mars 2020 Perseverance mission lifts off at the Kennedy Space Centre in Florida. The mission is part of the USA's largest moon to Mars exploration. Nasa will attempt to establish a sustained human presence on and around the moon by 2028 through their Artemis programme EPA World news in pictures 29 July 2020 A woman refreshes herself in a outdoor pool in summer temperatures in Ehingen, Germany dpa via AP World news in pictures 28 July 2020 Malaysia's former prime minister Najib Razak speaks to the media after he was found guilty in his corruption trial in Kuala Lumpur AFP via Getty World news in pictures 27 July 2020 North Korean leader Kim Jong Un poses for a photograph after conferring commemorative pistols to leading commanding officers of the armed forces on the 67th anniversary of the "Day of Victory in the Great Fatherland Liberation War". Which marks the signing of the Korean War armistice KCNA via Reuters

Shell believes the cells could remain "largely upright" for at least 1,000 years "despite being punctured and damaged".

Mr Manning admitted that what would happen to the structures in 250 years’ time was “not an absolute science”, partly because “we haven’t got reinforced concrete of that age”.

But he added: “The environmental impact of the oil sediment if and when it is eventually released … is very small. “The option of doing something is completely disproportionate to the environmental impact when eventually that sediment is released.”

Mr Manning said the cells and legs had been “built to withstand the very worst the North Sea can throw against them” and had not been designed to be refloated.

However, under the international OSPAR agreement, they are supposed to be removed and so Shell needs permission from the UK Government to leave them in the place.

Some oil in the storage cells will be removed under Shell's plan, leading behind the more viscous sediment, which is about 25 per cent oil with sand and water making up the rest. A Shell source said the sediment tended to occupy no more than a quarter of the storage cells.

The company admits that the legs will pose a hazard to shipping, mainly fishing boats, but plans to take steps to ensure fleets are aware of the potential hazard and say that the collision risk is low.

“There are 25,000 shipwrecks around the UK coastline,” Mr Manning said. “This is really a pin-prick when you think of the total size of the UK continental shelf. This is not a highly trafficked route in the North Sea, it’s not a key route from the UK to Norway.”

Lang Banks, the director of WWF Scotland, said the amount of oil in the cells and other structures was greater than allowed to be left after decommissioning under international standards.

“Oil and gas companies operating in the North Sea have a legal, as well as moral, obligation to clean-up their mess,” he said. “Having once pushed the boundaries of science and engineering to secure the oil and gas beneath the seabed, the industry should be pressed once again to do the same when decommissioning.

“The OSPAR agreement rules are there to make sure the marine environment is protected and those rules should be followed. The main thing preventing this from being done in this particular case is the cost. Shell should do the right thing and remove these potentially polluting materials.”

However he suggested WWF Scotland would not object to the legs being left in the sea if it was too dangerous to remove them. “The rules already allow for companies to seek permission to leave some material behind – such as the massive concrete legs – where moving it would pose an unacceptable risk to staff or the environment. We accept this principle,” Mr Banks said.

The Scottish Fishermen's Federation suggested in an emailed statement that it had some sympathy with Shell's hope to leave the legs standing.

"The SFF’s desire/policy in relation to oil and gas decommissioning in the UK continental shelf, taking into account current legislation and related guidelines, is as far as possible a return to a clean seabed," it said.

"We do, however, appreciate that there are safety concerns, technical considerations and cost implications involved in attempting to remove such structures.

"If the legs are to remain and cause an obstruction, as a general principle, the fishing view is that we should be able to see them."

After it has received Shell’s proposals, the Government will hold a public consultation before making its decision.