A closure assembly for a drinking cup, comprising: - an annular body mountable to an open upper end of a cup and having a rim to enable a user to drink liquid from said cup through the annular body, - a closure member within said body positionable so as to extend across the open upper end of the cup to which the body is mounted and having a plurality of apertures and a central opening therein, - a sealing element on an inner side of the closure member and an actuator on the opposite side of the closure member which is accessible to a user when said closure assembly is mounted to a cup, the sealing element and actuator being coupled to each other with the sealing element biased into a rest position in which it is urged against said inner side of the closure member and contacts said inner side with an upper side of the sealing element, which in the rest position runs parallel thereto, to block said apertures and prevent the flow of liquid therethrough, wherein the actuator comprises a lip contacting portion that extends over the closure member towards said rim on the annular body, the arrangement being such that the sealing element is moved out of said rest position to allow liquid to flow through said apertures and out of the cup when pressure sufficient to overcome said bias is applied to the lip contacting portion by a user, and - a biasing member to bias the sealing element into its rest position, wherein the closure member comprises a deformable diaphragm, wherein the biasing member is integrally formed with said deformable diaphragm and wherein the deformable diaphragm has a raised region surrounding the central opening that spaces the lip contacting portion from the apertures, said biasing member being formed from said raised region surrounding the central opening. - an annular body mountable to an open upper end of a cup and having a rim to enable a user to drink liquid from said cup through the annular body, - a closure member within said body positionable so as to extend across the open upper end of the cup to which the body is mounted and having a plurality of apertures and a central opening therein, - a sealing element on an inner side of the closure member and an actuator on the opposite side of the closure member which is accessible to a user when said closure assembly is mounted to a cup, the sealing element and actuator being coupled to each other with the sealing element biased into a rest position in which it is urged against said inner side of the closure member and contacts said inner side with an upper side of the sealing element, which in the rest position runs parallel thereto, to block said apertures and prevent the flow of liquid therethrough, wherein the actuator comprises a lip contacting portion that extends over the closure member towards said rim on the annular body, the arrangement being such that the sealing element is moved out of said rest position to allow liquid to flow through said apertures and out of the cup when pressure sufficient to overcome said bias is applied to the lip contacting portion by a user, and - a biasing member to bias the sealing element into its rest position, wherein the closure member comprises a deformable diaphragm, wherein the biasing member is integrally formed with said deformable diaphragm and wherein the deformable diaphragm has a raised region surrounding the central opening that spaces the lip contacting portion from the apertures, said biasing member being formed from said raised region surrounding the central opening.