EU heads and British Prime Minister Boris Johnson have agreed to assess progress on their talks for a post-Brexit trading relationship next week, an EU spokesman said on Thursday. "Following call with @BorisJohnson @eucopresident agreed to hold a high level conference in the afternoon of Monday June 15 with @vonderleyen and @DavidSassoli by videoconference," the spokesman for European Council chief Charles Michel wrote in a tweet. clp/fmi/spm/har