A method for forming a fiber-reinforced composite structure comprising the steps of: a) providing at least one preform comprising at least one first ply and at least one subsequent ply wherein each of said plies (12, 14) comprises a thermoset and/or thermoplastic resin matrix and fibers and wherein the direction of the fibers in said first ply is different from the direction of the fibers in said subsequent ply; b) helically winding said preform around a mandrel from a first end region of the mandrel to a second end region of the mandrel and/or from said second end region to said first end region, such that the direction of the fibers in the first ply is orientated relative to an axial direction defined by the mandrel so as to improve a certain performance; c) as an alternative to step b), helically winding at least two said preforms (10a, 10b) around the mandrel from said first end region of the mandrel to said second end region of the mandrel, one of said preforms being wound clockwise and the other of said preforms being wound counterclockwise, such that the direction of the fibers in the first ply of at least one of said preforms is orientated relative to the axial direction defined by the mandrel so as to improve a certain performance; d) repeating steps b) or c) until the successive windings of the preform define a specific three-dimensional structure; e) compacting with pressure said specific three-dimensional structure; f) consolidating said specific three-dimensional structure through the application of a heating cycle as required by the resin systems characterised in that: in step a) in the preform the fibers in said first ply are oriented in a direction which is inclined at an angle to the 0° direction relative to a longitudinal direction of the preform; in step b) the preform is helically wound such that the direction of the fibers in the first ply is parallel to the axial direction; and in step c) the preforms (10a, 10b) are helically wound such that the direction of the fibers in each first ply is parallel to the axial direction. a) providing at least one preform comprising at least one first ply and at least one subsequent ply wherein each of said plies (12, 14) comprises a thermoset and/or thermoplastic resin matrix and fibers and wherein the direction of the fibers in said first ply is different from the direction of the fibers in said subsequent ply; b) helically winding said preform around a mandrel from a first end region of the mandrel to a second end region of the mandrel and/or from said second end region to said first end region, such that the direction of the fibers in the first ply is orientated relative to an axial direction defined by the mandrel so as to improve a certain performance; c) as an alternative to step b), helically winding at least two said preforms (10a, 10b) around the mandrel from said first end region of the mandrel to said second end region of the mandrel, one of said preforms being wound clockwise and the other of said preforms being wound counterclockwise, such that the direction of the fibers in the first ply of at least one of said preforms is orientated relative to the axial direction defined by the mandrel so as to improve a certain performance; d) repeating steps b) or c) until the successive windings of the preform define a specific three-dimensional structure; e) compacting with pressure said specific three-dimensional structure; f) consolidating said specific three-dimensional structure through the application of a heating cycle as required by the resin systems characterised in that: in step a) in the preform the fibers in said first ply are oriented in a direction which is inclined at an angle to the 0° direction relative to a longitudinal direction of the preform; in step b) the preform is helically wound such that the direction of the fibers in the first ply is parallel to the axial direction; and in step c) the preforms (10a, 10b) are helically wound such that the direction of the fibers in each first ply is parallel to the axial direction. in step a) in the preform the fibers in said first ply are oriented in a direction which is inclined at an angle to the 0° direction relative to a longitudinal direction of the preform; in step b) the preform is helically wound such that the direction of the fibers in the first ply is parallel to the axial direction; and in step c) the preforms (10a, 10b) are helically wound such that the direction of the fibers in each first ply is parallel to the axial direction.