Sir Keir Starmer is meeting political leaders from both sides of the Irish border in Edinburgh.
He is only the third prime minister to attend a meeting of the British-Irish Council in 17 years.
It is attended by the Taoiseach (Irish prime minister) and Tánaiste (Irish deputy prime minister) Simon Harris and Micheál Martin just a week after a general election which has paved the way for another Fianna Fáil/Fine Gael coalition government.
Northern Ireland's First and Deputy First Ministers, Michelle O'Neill and Emma Little-Pengelly are also there, as will the first ministers of Scotland and Wales.