jump-up artist; jump-up merchant; jump-up man noun a criminal who steals from the back of goods-vehicles UK, 1951
Jump up on to a tailboard, climb up on the lorry or open the back door to a van, roll off whatever you see and hope to find something profitable in the wreckage [...] some kids formed gangs of “jump up” artists. — Brian McDonald, ElephantBoys, p. 37, 2000