A closure assembly comprising: a closure cap adapted to be fitted to the neck of a container to close the container, said cap comprising an upper wall and a cylindrical skirt depending there from, a reservoir being formed on the underside of the upper wall within the skirt and provided with a dispensing opening; and a closing member to close the dispensing opening of the reservoir; the closing member comprising - a fixing member, the fixing member being adapted to fit into the neck of the container, when the assembly is fitted thereto, with an interference fit - a plug member, the plug member being adapted to fit into an open end of the reservoir to close the reservoir when the closure cap and closing member are fitted together, - a passage element, allowing material to be dispensed from the reservoir into the container, the interference fit being such that when the closure cap is removed from the container, the closing member remains held within the neck of the container and is separated from the closure cap so that the dispensing opening is opened and material contained therein is dispensed into the container, characterised in that the closure cap is provided with sealing means (12, 26, 27) for directly sealing against the neck of such container, in particular with an annular wall extending downwardly from the underside of the upper wall of the closure cap to fit sealingly into the neck of the container, wherein an upper end of the fixing member rests below the upper rim of the container neck. a closure cap adapted to be fitted to the neck of a container to close the container, said cap comprising an upper wall and a cylindrical skirt depending there from, a reservoir being formed on the underside of the upper wall within the skirt and provided with a dispensing opening; and a closing member to close the dispensing opening of the reservoir; the closing member comprising - a fixing member, the fixing member being adapted to fit into the neck of the container, when the assembly is fitted thereto, with an interference fit - a plug member, the plug member being adapted to fit into an open end of the reservoir to close the reservoir when the closure cap and closing member are fitted together, - a passage element, allowing material to be dispensed from the reservoir into the container, the interference fit being such that when the closure cap is removed from the container, the closing member remains held within the neck of the container and is separated from the closure cap so that the dispensing opening is opened and material contained therein is dispensed into the container, characterised in that the closure cap is provided with sealing means (12, 26, 27) for directly sealing against the neck of such container, in particular with an annular wall extending downwardly from the underside of the upper wall of the closure cap to fit sealingly into the neck of the container, wherein an upper end of the fixing member rests below the upper rim of the container neck. - a fixing member, the fixing member being adapted to fit into the neck of the container, when the assembly is fitted thereto, with an interference fit - a plug member, the plug member being adapted to fit into an open end of the reservoir to close the reservoir when the closure cap and closing member are fitted together, - a passage element, allowing material to be dispensed from the reservoir into the container, the interference fit being such that when the closure cap is removed from the container, the closing member remains held within the neck of the container and is separated from the closure cap so that the dispensing opening is opened and material contained therein is dispensed into the container, characterised in that the closure cap is provided with sealing means (12, 26, 27) for directly sealing against the neck of such container, in particular with an annular wall extending downwardly from the underside of the upper wall of the closure cap to fit sealingly into the neck of the container, wherein an upper end of the fixing member rests below the upper rim of the container neck.