Apparatus for moving a trailer comprising a trailer drive unit and a mounting mechanism for securing the trailer drive unit to a trailer, the trailer drive unit comprising: drive means , a first lateral roller , a second lateral roller , and drive transmitting means located between the first lateral roller and the second lateral roller ; wherein the drive transmitting means receives drive from the drive means and transmits the drive to the first lateral roller and the second lateral roller , wherein the first lateral roller and the second lateral roller are arranged to rotate about a communal drive shaft , and wherein the first lateral roller and the second lateral roller are arranged to move in an engagement direction between a first position and a second position, and, in which, in the second position, the first lateral roller and the second lateral roller are arranged to be urged against a same ground contacting surface of a single wheel in order to transmit drive from the drive means to the wheel , characterised in that : the drive transmitting means transmits drive to the communal shaft and the communal shaft receives drive from the drive transmitting means at a position located between the first lateral roller and the second lateral roller ; and the communal shaft comprises a central engaging portion located between the first lateral roller and the second lateral roller , wherein the central engaging portion receives drive from the drive means . drive means , a first lateral roller , a second lateral roller , and drive transmitting means located between the first lateral roller and the second lateral roller ; wherein the drive transmitting means receives drive from the drive means and transmits the drive to the first lateral roller and the second lateral roller , wherein the first lateral roller and the second lateral roller are arranged to rotate about a communal drive shaft , and wherein the first lateral roller and the second lateral roller are arranged to move in an engagement direction between a first position and a second position, and, in which, in the second position, the first lateral roller and the second lateral roller are arranged to be urged against a same ground contacting surface of a single wheel in order to transmit drive from the drive means to the wheel , characterised in that : the drive transmitting means transmits drive to the communal shaft and the communal shaft receives drive from the drive transmitting means at a position located between the first lateral roller and the second lateral roller ; and the communal shaft comprises a central engaging portion located between the first lateral roller and the second lateral roller , wherein the central engaging portion receives drive from the drive means . the drive transmitting means transmits drive to the communal shaft and the communal shaft receives drive from the drive transmitting means at a position located between the first lateral roller and the second lateral roller ; and the communal shaft comprises a central engaging portion located between the first lateral roller and the second lateral roller , wherein the central engaging portion receives drive from the drive means . <EOS>