6 Down is " Everybody, say, on European border ... . Answer obvious " allege", but "border" seems to have no connection.
8 Down is ".... check arresting a border leader " Answer "caliph" and here "border" is "lip" but no help with the " allege" border.
As I wrote, I got the answers immediately but cannot see how "allege"is a "border" which is usually the cryptic synonym you are looking for. E.g. caliph is a leader in some Eastern country.