Michel Barnier, the EU's former chief Brexit negotiator, spoke at a Chatham House event marking a decade since Brexit — and the moment arrived with a measurably different public mood on both sides of the Channel.

Barnier has maintained a clear position: security and defence should not be treated as bargaining chips in trade talks. He stated this explicitly in May 2018 and has held the line since. That stance carries fresh importance now. The EU Institute for Security Studies documented in June 2021 what the bloc discovered after departure: the UK's military capabilities, intelligence assets, and diplomatic resources had been structural load-bearers in European defence architecture. Brussels has not replaced them. Any renewed security cooperation, then, is not a concession but a response to a genuine capability gap.

The Opinion Shift

The political landscape has moved. John Curtice's June 2026 analysis for UK in a Changing Europe found that a growing majority of British voters now regard the Leave vote as the wrong call. The shift spans generations: a majority of Gen Z believe Brexit has failed, with substantial backing for a new EU membership referendum. Statista polling confirms the trend — the share of Britons who regret Brexit has climbed steadily since formal departure.

European voters show signs of openness. European Council on Foreign Relations polling published on 20 June 2026 found many EU citizens view Britain positively — significant if a future British government tests appetite for deeper EU engagement. Hostility toward the UK within EU member states had been a quiet structural barrier to rapprochement; that obstacle appears less daunting than in 2020.

The Domestic Political Complication

Labour's position adds friction to the picture. A BBC report from March 2026 noted that Labour's approach to Brexit has shifted in ways that concern party strategists about electoral standing with Leave voters. This is the bind any governing party faces when public mood is drifting toward regret: the Leave coalition is not uniform, and moves toward the EU risk alienating swing constituencies in the English Midlands and North — regions that shaped electoral maps in 2019 and 2024.

The numbers matter. Curtice's data shows aggregate opinion is moving, but aggregate and swing-constituency opinion are different measures. A government that shifts on EU relations faster than its political coalition can bear risks the same structural punishment Conservatives faced when they failed to deliver on the opposite expectation a decade earlier.

What Barnier's Appearance Signals

Barnier's Chatham House presence is not accidental. He retains credibility on both sides of the Channel after four years navigating the EU's most technically demanding bilateral negotiation. His renewed visibility and his restatement that security must not be traded against market access suggest interest in shaping the terms of any future conversation.

The sequencing problem is the hardest one. The EU's standard line has been that deeper market access requires regulatory alignment; London has resisted framing any new engagement as regulatory alignment by stealth. If both sides accepted Barnier's case for separating security from commercial leverage, one practical path emerges: a UK-EU security and defence agreement pursued independently of Single Market questions. This would address the capability gap Brussels identified while allowing Westminster to avoid the politically fraught framing of 'rejoining.'

Whether Labour is willing or able to move in that direction before the next election remains unclear. But the past month's data — Curtice's polling, the ECFR findings, Barnier's remarks — makes one thing plain: the structural opening for re-engagement is wider now than at any point since 2016. Whether the political will exists to move through it is another question entirely.