A release coating composition is prepared comprising a polyorganosiloxane (A) having alkenyl groups, a crosslinking agent (B) having organohydrogensiloxane groups, a catalyst for the hydrosilylation reaction between (A) and (B), and an anchorage additive for enhancing the adhesion of the composition to a polymer film substrate. The anchorage additive is the reaction product of a fluid polyorganosiloxane (C) containing at least one alkenyl group and at least one silanol group with a hydrolysable silane (D) containing at least one epoxide group. The curable silicone release coating composition can be applied to a substrate known as a ‘liner’ retaining a label, which liner can for example be paper or a polymer film, and cured.