European Union trade deals must be ratified by all member states, the EU's highest court ruled, with possible consequences for Brexit.

Britain hopes to win a fast-track trade deal with Europe after it negotiates its divorce from the EU but the decision by the European Court of Justice could cripple that plan.

In a closely watched decision, the EU court said that any trade deal that includes a non-court dispute settlement system would require ratification by the EU's 38 national and regional authorities.

"It follows that the free trade agreement can, as it stands, only be concluded by the EU and the Member States jointly," the court said in a statement.

The decision applied to an EU-Singapore treaty signed in 2013, but will stand as key jurisprudence for future trade deals including any deal with Britain.

Non-government arbitration systems are a core part of international trade deals and have drawn fierce opposition by activists who see them as being under the influence of corporate interests.

Last year the tiny region of Wallonia almost killed off a huge EU-Canada trade deal after years of talks, because of its opposition to this system.

That tussle highlighted the dangers of a marathon ratification process that involves high-tension votes in national or regional parliaments.

The European Commission, which handles trade negotiations for the EU, saw the Singapore deal as a new standard that reflected bigger powers won by Brussels.

In the commission's big plans, the Singapore deal would have only required the greenlight of the European Council, which groups officials and ministers from the EU's 28 governments, and the European Parliament.

British Prime Minister Theresa May has insisted that Britain could negotiate its departure from the European Union and a new trading arrangement within two years.

The EU-Canada accord took seven years to negotiate and has only begun the long national approval process.