Greenpeace argued that sinking the Spar would be an environmental crime, and set a dangerous precedent. It should be brought ashore, broken up and recycled, creating jobs in the process.

But the evidence suggests that Greenpeace is wrong and Shell is right - as is the Government in granting permission for sea dumping. The best thing to do with the skyscraper-sized structure is to drop it 6,000ft deep, where it will slowly break up over thousands of years.

The Spar was, essentially, an oil tanker filling station, storing crude from Shell and Esso's Brent field. A hundred tonnes of oily, silty sludge lie in the bottom of six big storage tanks. This sludge contains several kilogrammes of toxic heavy metals such as cadmium, lead and mercury. The tanks and pipework are coated with mildly radioactive salts from the underground oil reservoirs.

Shell's scientists say the radiation and poisonous substances will only kill seabed creatures very close to the Spar. The effects will extend a few hundred yards at most. Thanks to the colossal dilution powers of the ocean, wider marine life such as surface-dwelling fish, and man, will be unaffected.

This is credible. But why not err on the side of caution, and dispose of the Brent Spar on land?

First, that would cost about pounds 34m more. Most of this would be met by the taxpayer: oil companies claim generous tax relief against decommissioning North Sea structures.

Second, disposal on land presents its own hazards.The Brent Spar has asbestos in its upper desks. With sea dumping, there is no risk of fibres being breathed in. Asbestos is not known to be harmful to marine life.

The saddest aspect of the campaign is that it may divert attention from more important sources of pollution in the North Sea, and its overfishing - the single most important cause of environmental damage to the sea life around Britain.