To be anally technical it USED to end in Leeds (city centre, junction 47) but has been extended and officially ends when it joins the A1 (which is a completely different road/motorway andjac), just north of Garforth
To be anally correct, the M1 does indeed now join up with the A1; not quite in the middle of a stretch that was completely rebuilt to motorway standard and renumbered A1(M) You would have to pay close attention to see the join. After three miles (or so) it reverts to the A1. With two more stretches of motorway on the way, the A1 eventually reaches Edinburgh.