A method of injection moulding an article, the method comprising the steps of: (a) providing an injection mould comprising first and second mould parts (6, 20), and having at least one movable portion of one of the first and second mould parts(6, 20); (b) disposing the first and second mould parts in a fully closed configuration so as to define a mould cavity therebetween for moulding an article, in the fully closed configuration the first and second mould parts (6, 20) defining a cavity outer surface which defines the outer shape of the article to be moulded in the mould cavity; (c) injecting molten material into the cavity, at an injection apparatus filling pressure applied by the injection apparatus, at an injection inlet of the cavity; (d) during the injecting step, moving at least one movable portion of one of the first and second mould parts (6, 20) from a forward position, defining the article to be moulded, to a rearward position by pressure of the injecting molten material thereby to increase the volume of the mould cavity in the fully closed configuration and to reduce the flow length/thickness ratio of the cavity; (e) filling the mould cavity with the molten material; and (f) after filling the mould cavity, returning the at least one movable portion from the rearward position to the forward position by an applied external pressure, applied by an actuator wherein the actuator pressure is less than 20 bar, thereby expelling excess molten material back through the injection inlet against a low holding phase pressure applied to the injected material by the injection apparatus, the holding phase pressure being selected to accommodate shrinkage of the injected material within the mould during cooling, the mould surface being restored to its original forward position, wherein after the injected material has solidified, the applied external pressure is reduced during cooling of the injected material. (a) providing an injection mould comprising first and second mould parts (6, 20), and having at least one movable portion of one of the first and second mould parts(6, 20); (b) disposing the first and second mould parts in a fully closed configuration so as to define a mould cavity therebetween for moulding an article, in the fully closed configuration the first and second mould parts (6, 20) defining a cavity outer surface which defines the outer shape of the article to be moulded in the mould cavity; (c) injecting molten material into the cavity, at an injection apparatus filling pressure applied by the injection apparatus, at an injection inlet of the cavity; (d) during the injecting step, moving at least one movable portion of one of the first and second mould parts (6, 20) from a forward position, defining the article to be moulded, to a rearward position by pressure of the injecting molten material thereby to increase the volume of the mould cavity in the fully closed configuration and to reduce the flow length/thickness ratio of the cavity; (e) filling the mould cavity with the molten material; and (f) after filling the mould cavity, returning the at least one movable portion from the rearward position to the forward position by an applied external pressure, applied by an actuator wherein the actuator pressure is less than 20 bar, thereby expelling excess molten material back through the injection inlet against a low holding phase pressure applied to the injected material by the injection apparatus, the holding phase pressure being selected to accommodate shrinkage of the injected material within the mould during cooling, the mould surface being restored to its original forward position, wherein after the injected material has solidified, the applied external pressure is reduced during cooling of the injected material.