By Roger Harrabin BBC environment analyst: ‘They have been urging for a new global treaty to tackle the problem.

But a new report – to be presented to a Royal Geographical Society conference on Tuesday – says littering the sea with plastics is already prohibited under existing agreements.

The report urges those governments that are trying to tackle the issue to put legal pressure on those that are not.   The paper (downloadable PDF) has been written by the veteran environment journalist Oliver Tickell.

Mr Tickell’s principal conclusion is backed by ClientEarth, the legal group that successfully sued the UK over failures to meet air pollution laws.

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The journalist says legal action against big polluters such as China, India and Indonesia can be taken only by a nation state. So he calls for governments and green groups to support small island nations suffering most from plastic pollution. Tickell maintains that marine plastic litter can already be controlled through the United Nations Convention on the Law of the Sea (UNCLOS); the London Convention; the MARPOL Convention; the Basel Convention; Customary Law, and many other regional agreements.

Article 194 of UNCLOS, for instance, requires states to “prevent, reduce and control pollution of the marine environment from any source. “Measures shall include, inter alia, those designed to minimize to the fullest possible extent… the release of toxic, harmful or noxious substances, especially those which are persistent, from land-based sources… [and] shall include those necessary to protect and preserve rare or fragile ecosystems as well as the habitat of depleted, threatened or endangered species and other forms of marine life.” Click here to read more