An accessory mounting system for a vehicle, comprising: an accessory support including a first wall portion defining an outer support surface and an inner support surface; and a fastening device for fastening an accessory to the accessory support, comprising; a first structure and a clamping formation arranged to engage with the inner support surface so as to clamp the accessory support between the clamping formation and the first structure of the fastening device, the clamping formation comprising a resilient member; characterized in that the resilient member is placed into a compressed condition when the fastening device is engaged with the accessory support; and wherein the resilient member comprises a cam feature having a profiled outer surface that defines a first contact region for bearing against the inner support surface of the accessory support in the region of the first wall portion and a second contact region for bearing against the inner support surface of the accessory support in the region of a second wall portion; and a further surface extending obliquely between the first and second contact regions (53, 52), wherein, during use, the fastening device is configured to pivot about the cam feature so that the fastening device engages onto the accessory support, during which movement of the cam feature transitions from the oblique further surface being in contact with the inner support surface of the accessory support, to the second contact region being in contact with the inner support surface about a transition edge so that the fastening device snaps into engagement with the accessory support. an accessory support including a first wall portion defining an outer support surface and an inner support surface; and a fastening device for fastening an accessory to the accessory support, comprising; a first structure and a clamping formation arranged to engage with the inner support surface so as to clamp the accessory support between the clamping formation and the first structure of the fastening device, the clamping formation comprising a resilient member; characterized in that the resilient member is placed into a compressed condition when the fastening device is engaged with the accessory support; and wherein the resilient member comprises a cam feature having a profiled outer surface that defines a first contact region for bearing against the inner support surface of the accessory support in the region of the first wall portion and a second contact region for bearing against the inner support surface of the accessory support in the region of a second wall portion; and a further surface extending obliquely between the first and second contact regions (53, 52), wherein, during use, the fastening device is configured to pivot about the cam feature so that the fastening device engages onto the accessory support, during which movement of the cam feature transitions from the oblique further surface being in contact with the inner support surface of the accessory support, to the second contact region being in contact with the inner support surface about a transition edge so that the fastening device snaps into engagement with the accessory support.