The “Brexit” debate goes on. Enter Jean-Claude Piris, who for 22 years was legal chief at the European Council, which represents European leaders and governments. Piris is not to be confused with two other Jean-Claudes, Juncker or Trichet. But his observations are salutary.

A London think tank, the Centre for European Reform, has published a 13-page paper by Piris in which he examines “the seven alternatives to EU membership” if Britain votes to leave. Put gently, this is code for seven shades of strife. Piris presents Brexit on a panorama beset with practical, political, economic and legal difficulty.

An exit would pull London in one of two directions, he argues. In one, Britain becomes a kind of EU satellite obliged to transpose into domestic law EU regulations and directives for the single market.

In the other, Britain suffers from higher barriers with its main market, obliging London to start trade negotiations from scratch with the EU and the rest of the world “without having much bargaining power”.

None of that comes as a surprise in an Irish context, where anxiety about the potential for distress is widespread. Just as Dublin warns of new Border controls with the North, Piris points to that possibility if London sought to become “just another partner” of the EU under World Trade Organisation rules.

“The UK would have to re-establish customs controls at borders with EU member states. This would include establishing a border with the Republic of Ireland, unless the EU and the UK managed to conclude a special agreement on that issue before the date of the UK’s withdrawal.”

Piris sees no purchase for special status as a “half-member” of the union, an option favoured by many Eurosceptics. He casts this as an impossibility, saying the EU would have to concede advantages consistently refused to Norway, Switzerland and others. He also notes that the treaty change required to facilitate such a departure “may mean a referendum in member states such as Ireland”.

There is more but you get the picture.