Activists have pushed the boundaries to get their points across

Activists from the Netherlands, Germany and Denmark boarded two oil platforms in the North Sea on Monday.

The protest action was led by Greenpeace at Shell’s Brent field, around 115 miles north-east of Shetland.

The climate group spent the night aboard the decommissioned Brent Bravo, brandishing signs reading: “Shell, clean up your mess”.

It halted its protest action after 24 hours, leaving a graffiti slogan labelling the platform “toxic waste”.

It comes ahead of a special meeting of Ospar, an agreement between 15 governments to protect Europe’s marine environment, which takes place in London tomorrow.

Some countries have lodged objections to Shell’s plans to leave the legs of three of the Brent platforms – Bravo, Charlie and Delta – in the sea, with concerns around the contents of concrete oil storage cells within them deteriorating. Shell insists its plans are both safe and “environmentally sound”, with any release of the cells’ contents happening gradually over centuries.

In June, a North Sea stand-off between Greenpeace and oil giant BP lasted 12 days.

Activists scaled the Transocean-owned Paul B Loyd Jr drilling rig, preventing it from reaching BP’s oil-rich Vorlich field.

The platform was forced to halt its journey several times as the campaigners blocked its path with an icebreaker ship and inflatable launches.

The stand-off between the two organisations is understood to have cost BP more than £1.5 million.

A number of arrests were made in the Cromarty Firth when Greenpeace activists boarded the rig and attached themselves to it.

Greenpeace demanded that BP cease from drilling more wells and transition to renewable energy.