How Brent Spar will be dismantled: 3D graphic explained by Eric Faulds of Shell

A huge barge crane started the hour-long task of taking down 1,600 tonne oil storage tanks late on Wednesday afternoon.

The sheer size of the operation delayed an earlier start, said owners Shell Expo.

The 135m high structure is sited in a deepwater construction site at Vats in Norway, after being moved from Erfjord in August this year.

Shell Expo plans to recycle the whole structure, which will be taken apart over six months.

Eventually, the scrap will be used to build the foundations of a new ferry terminal.

The operation to remove what used to be staff living quarters was being achieved with one of the world's largest semi-submersible crane vessels, named the Thialf.

The lifting is being carried out under floodlights.

Shell spokeswoman Mary Brennan said: "As the module is gradually raised, the rest of the Spar will also rise in the water about seven metres as the load is removed, giving an impression that the whole structure is being lifted.

A Norwegian fjord has been the Spar's home for three years

"When lifted well clear of the Spar's hull, the the topsides will be swung around and placed on the Thialf's deck."

The remaining part of the hull - which is longer than a football pitch - will be gradually floated to the water's surface and cut into rings which will be used in the construction of the quay alongside the south-eastern Norwegian town of Stavanger.

The disposal plan - hailed as a "unique re-use solution" by the company - follows a long campaign by environmentalists to stop the rig being dumped at sea.

In 1995 environmentalists from Greenpeace occupied Brent Spar to prevent Shell going through with their original plan.

The destruction of the rig will cost Shell �43m in total, compared to the �4.5m cost of dumping.

The structure, and the headaches it caused, are massive

The dismantling has been delayed for months, but the work is expected to be completed at the end of next year.

Energy minister John Battle has said the plan to dispose of Brent Spar is an "acceptable environmental solution".

Greenpeace oil expert Jan Rispens is delighted with the plan.

"This is the best possible solution of what to do with the Brent Spar," he said.

"It protects the oceans, it creates jobs and it reuses the material."

Brent Spar had been used as a loading buoy and storage tank for crude oil for 15 years, until it was decommissioned in 1991.

An environmental outcry ensued when it emerged that Shell Expro was planning to sink the structure in the Atlantic Ocean.

As well as Greenpeace's occupation of the rig off the Scottish coast, many people boycotted Shell products, a campaign the company said lost it millions of dollars.

The BBC's Nikki Albon: New lease of life for rusting oil platform

One Shell station in Germany was firebombed, an action condemned by Greenpeace.

The publicity led the oil company to drop its plans in 1995 and no oil structures have been dumped at sea since then.

In July this year European nations agreed to ban the dumping of offshore steel oil rigs at a conference on sea pollution attended by environment ministers from 15 countries.