More than six years after the UK voted to leave the EU, you'd think the process would be over by now. Think again.

Unfortunately, the Northern Ireland protocol — no hard border with the Republic of Ireland, an EU member state — remains a Brexit "hangover" that's causing a lot of frustration across the English Channel, former British PM Tony Blair tells Ian Bremmer on GZERO World.

What's getting in the way of a constructive relationship between Brussels and London? For Blair, the very anti-European politics of part of the UK right.

Blair, who wanted to remain in the EU, doesn't think Brexit will end up fragmenting the country. But he admits Brexit has given fresh impetus to both Scottish nationalists and those who want a united Republic of Ireland.

The video above is an excerpt from the weekly show, GZERO World with Ian Bremmer, which airs weekly on US public television. Watch the episode on "upheaval in UK" here.