Why Greenpeace is dropping huge boulders into the sea

A Greenpeace ship has been dropping huge boulders into the sea off Brighton this week to stop fishing boats from trawling the sea bed. 

The action is part of campaign to tighten restrictions on the most destructive forms of fishing in protected areas of UK waters. 

But leaders of the fishing community describe the action as dangerous, illegal and irresponsible. 

Chief environment correspondent Justin Rowlatt reports.