THE President of the European Commission has warned “economic nationalism” is inconsistent with the EU and the prosperity of its people on the eve of Theresa May triggering Article 50.

Jean-Claude Juncker said the EU must not “revert to isolationism and protectionism” and warned its nations would “continue to show our teeth” if foreign companies tried to undercut EU traders.

The Prime Minister is expected to formally trigger the Brexit process within a fortnight, and will be keeping a close eye on the EU’s developing policy towards external countries.

Jean-Claude Juncker: There can be no place for economic nationalism in Europe of the future

She has pledged to withdraw from the single market and negotiate a bespoke ‘Great British Brexit’ to ensure Britain can continue to trade with Europe states, while her Chancellor has warned of a new, lower tax UK economic model if Brexit negotiations go sour.

Writing in The Herald, Mr Juncker said the EU would continue to need investment from abroad.

“That requires us to remain open for business, and keep foreign markets open to European business,” he said.

“But I am not a naïve free trader. We need to continue to show our teeth, taking measures against unfair trade practices like we did when imposing anti-dumping duties on Chinese steel, sweet corn from Thailand, or biodiesel from the US, Indonesia and Argentina.”

Jean-Claude Juncker: There can be no place for economic nationalism in Europe of the future

An anti-dumping duty is a protectionist tariff that a domestic government imposes on foreign imports that it believes are priced below fair market value.

Mr Juncker’s pledge to keep keep foreign markets open to European business will be welcomed by Westminster, but his tough stance against "unfair" trading is a reminder that non-EU states can be hit with protectionist tariffs.

Mr Juncker added: “With more than 50 per cent of EU businesses already part of global value chains, we cannot afford to revert to isolationism and protectionism.

“Our industry and economy depends on free, fair and sustainable international trade. Take the recent trade agreement reached with Canada, one of our most like-minded partners.

“It is the most progressive trade deal we have ever signed and it will have a transformative effect: exports to Canada already support around 900,000 European jobs and by removing tariffs we will help our businesses save over €500m [£434m] a year.”

He called for “an honest and open debate" on how much the EU can “harness globalisation, for example in the areas of fiscal, education or social policy”.

He said: “One thing is clear to me: I can see no scenario whatsoever in which economic nationalism can be consistent with the idea of Europe or with the prosperity of its people.

Jean-Claude Juncker: There can be no place for economic nationalism in Europe of the future

I believe in a Europe with a common, robust industrial policy, which ensures success even in challenging times. This policy plays a central role in the Europe that I am fighting for.”

The son of steelworker, he also urged regions with declining industries to prioritise local jobs over gentrification.

“Our regions and their old industrial sites should be transformed not just to create expensive riverside apartments but also to create new jobs for local workers.”