Image copyright Getty Images Image caption The Irish border is one of three main priorities in UK-EU Brexit talks

Amid a week of slow progress in the Brexit talks, the discussions on Ireland appear to have been the most productive.

'Useful' 'constructive' and 'clarifying' are other ways they have been described.

EU chief negotiator Michel Barnier said there had been "genuine progress" on the common travel area (CTA)

While the Brexit Secretary, David Davis, said there was a 'high degree of convergence' on that issue.

Image copyright Reuters Image caption The UK and EU have agreed a joint 'scoping exercise' on impact of Brexit on cross-border institutions

This maybe shouldn't come as a surprise - if anything was to be resolved quickly it was going to be the CTA

It is an arrangement between the UK and Ireland which pre-dates the formation of the EU.

It allows passport-free travel between the UK and Ireland and gives British and Irish citizens a range of rights in each other's countries.

It also means the two countries cooperate closely on immigration matters.

Both governments say its preservation is a red line issue and the EU has been sympathetic to that view.

Media playback is unsupported on your device Media caption Follow the road that cuts across the Irish border four times inside six miles

However the EU wanted to be clear that Ireland's role in the CTA would not be used to interfere with the free movement rights of other EU citizens.

That meant it wanted a guarantee that Ireland would not be expected to act as a gatekeeper for the U.K. by stopping other EU citizens travelling from the Republic of Ireland into the Northern Ireland and beyond.

The UK effectively gave that guarantee in its Northern Ireland position paper and reiterated it during a presentation this week.

Final agreement on the CTA may depend on the wider question of how the UK and the EU share data after Brexit, but that has not been flagged as a major sticking point.

Image copyright Pacemaker Image caption The government has repeatedly said it does not want to go back to the borders of the past

On other cross border issues and the institutions of the Good Friday Agreement it is clear that there is a lot more work to be done.

The totality of cross border institutions and relationships has not yet been defined nor has there been a substantial analysis of how Brexit could impact on them.

So to that end the UK and EU have agreed a joint 'scoping exercise.'

It is being described as a substantial piece of technical work which will take months rather than weeks to complete.

Image copyright Reuters

The Irish government is of course taking a close interest in all this and would like to see the UK turning its aspirations to protect cross border cooperation into workable solutions.

The Irish Foreign Minister, Simon Coveney, touched on that in a speech in Belfast this week.

He repeated his view that the most workable solution of all is for the UK to remain in the single market and a customs union.