A gas turbine engine comprising: a plurality of variable guide vanes (24, 26); a unison ring formed as a hollow ring with a cross section that is rectangular with curved corners; a lever arrangement connecting the unison ring to at least one of the variable guide vanes (24, 26), wherein the lever arrangement comprises a lever pin received by the unison ring; and a bush provided between the lever pin and the unison ring, wherein the bush comprises a first sprung region biased outwardly away from the lever pin towards the unison ring and adjacent the unison ring at a position proximal to a connection of the lever arrangement with the variable guide vanes; wherein the bush comprises a first retention protrusion adjacent an inner surface of the unison ring and proximal to connection of the lever arrangement to the variable guide vanes (24, 26) wherein the first retention protrusion is defined by an outer surface of the sprung region, wherein the bush comprises a second retention protrusion adjacent an outer surface of the unison ring and proximal to a connection of the lever arrangement to the variable guide vanes (24, 26); wherein the bush comprises a third retention protrusion adjacent an inner surface of the unison ring and distal to a connection of the lever arrangement to the variable guide vanes (24, 26), and wherein the bush comprises a fourth retention protrusion adjacent an outer surface of the unison ring and distal to a connection of the lever arrangement to the variable guide vanes (24, 26), wherein the bush comprises a further sprung region biased outwardly away from the lever pin towards the unison ring, and wherein the further sprung region is adjacent the unison ring at a position distal to a connection of the lever arrangement with the variable guide vanes (24, 26). and wherein the unison ring defines a first hole proximal to the connection of the lever arrangement with the variable guide vanes (24, 26) and a second hole distal to the connection of the lever arrangement with the variable guide vanes (24, 26), the lever pin and bush being received through the first hole and the second hole. a plurality of variable guide vanes (24, 26); a unison ring formed as a hollow ring with a cross section that is rectangular with curved corners; a lever arrangement connecting the unison ring to at least one of the variable guide vanes (24, 26), wherein the lever arrangement comprises a lever pin received by the unison ring; and a bush provided between the lever pin and the unison ring, wherein the bush comprises a first sprung region biased outwardly away from the lever pin towards the unison ring and adjacent the unison ring at a position proximal to a connection of the lever arrangement with the variable guide vanes; wherein the bush comprises a first retention protrusion adjacent an inner surface of the unison ring and proximal to connection of the lever arrangement to the variable guide vanes (24, 26) wherein the first retention protrusion is defined by an outer surface of the sprung region, wherein the bush comprises a second retention protrusion adjacent an outer surface of the unison ring and proximal to a connection of the lever arrangement to the variable guide vanes (24, 26); wherein the bush comprises a third retention protrusion adjacent an inner surface of the unison ring and distal to a connection of the lever arrangement to the variable guide vanes (24, 26), and wherein the bush comprises a fourth retention protrusion adjacent an outer surface of the unison ring and distal to a connection of the lever arrangement to the variable guide vanes (24, 26), wherein the bush comprises a further sprung region biased outwardly away from the lever pin towards the unison ring, and wherein the further sprung region is adjacent the unison ring at a position distal to a connection of the lever arrangement with the variable guide vanes (24, 26). and wherein the unison ring defines a first hole proximal to the connection of the lever arrangement with the variable guide vanes (24, 26) and a second hole distal to the connection of the lever arrangement with the variable guide vanes (24, 26), the lever pin and bush being received through the first hole and the second hole.