The European Union will have to develop a framework in which some core member states can do everything together and others will be less involved, Jean-Claude Juncker, EU commission president, said on Wednesday (18 November).

"I think that, eventually, it will no longer be possible that 33, 34 or 35 states will proceed at the same speed with the same momentum in the same direction,” Juncker said in a discussion with citizens in Brussels.

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The 28-member EU is in accession talks with countries in the Balkans with the aim of having them join the bloc eventually. Juncker said at the start of his presidency, however, that there will be no enlargement under his mandate until 2019.

Of the 28 EU countries, some already work more closely together on certain issues than they do with others.

Most notably, the 19 member states that share the euro currency coordinate budget policies and have a banking union in which all the large eurozone banks are under a single supervisor, the European Central Bank.

They also have a common method of winding down failed banks with a joint fund to cover the costs. The Schengen states, meanwhile, share a common external border and have dismantled border checks amongst themselves.

Juncker added that the EU should reconsider its organisation to make sure members may share policies at different speeds, if they wish, Reuters reported.

"One day we should rethink the European architecture with a group of countries that will do things, all things, together, and others that will position themselves in an orbit away from the core," Juncker said.

His predecessor, Jose Manuel Barroso, former EU commission president, opposed allowing a split within the EU and creating core and non-core EU countries – a two-speed Europe.

Speaking at the event, Juncker also declared: “Brexit will not happen”.

He added: “I spent three years of my life to avoid Grexit. I will not spend three years of my life to facilitate Brexit.”

British prime minister David Cameron is aiming to secure economic safeguards for non-eurozone countries during the UK membership negotiations with Brussels and wants to be excluded from an “ever closer union”, a principle enshrined in the EU treaty.

Juncker also said on Wednesday that the commission is planning to present next year a proposal on “common, minimum social rights to be applied in all member states”.

Juncker also reinstated his call for a European army and argued for a common defence policy in the EU.