The EU and Britain will need strong defence and security cooperation after London pulls out of the bloc, according to Michel Barnier, the French politician tasked with leading the Brexit negotiations.

"One thing I am sure of is, as far as defence and security matters are concerned, we must and we will need to build strong and biltateral cooperation," Barnier said Wednesday during a conference on the European Union's post-Brexit security policies.

Barnier, named in July as the European Commission's chief Brexit negotiator, said he understood the British government and its political opposition "are in the same spirit, to keep the link".

Barnier said he could not begin to describe future EU-British relations as he was still pulling his team together and meeting officials from the various governments.

He takes up his position on October 1 but the Brexit talks can only begin once Britain invokes Article 50 of the Lisbon treaty, which sets the clock ticking on two-years of divorce talks. That is not expected to begin until next year.

Britain's June 23 vote to quit the 28-nation European Union shocked EU leaders who had bet on a vote to remain.

Barnier, 65, held the key European Commission financial services portfolio from 2010 to 2014, spearheading efforts to tame the eurozone debt crisis which nearly brought down the single currency project.

He was central to efforts to save the EU's stricken banks, laying down tough rules to police a new banking union system which often put him at loggerheads with the City of London, one of the world's top financial markets.

Barnier was also closely linked to curbing banker bonuses, which were widely blamed for encouraging the risk-taking culture that ultimately left the banks over-stretched and in need of massive government bailouts costing billions.

Barnier told BFM TV in France shortly after the Brexit vote that the outcome was a loss for all but stressed the common interests, "especially in everything that touches upon our collective security".

Barnier has served as an adviser to Commission chief Jean-Claude Juncker on security issues as the EU reels from a series of deadly attacks claimed by Islamic State jihadis.