A method for controlling tyres or semi-finished products in a tyre production line, the method comprising: - lighting with a light radiation at least one portion of the surface of a tyre or semi-finished product to be inspected; - detecting the optical intensity of the light radiation reflected by said surface portion on a number N of pairs of polarisation states belonging to a group of three pairs of polarisation states corresponding to three pairs of points on Poincaré sphere, the three pairs of points being located at the opposite ends of three respective diameters of the Poincaré sphere orthogonal to each other, said number N being equal to 1 or 2 or 3; - calculating, on said surface portion, a number M of values representative of an equivalent number of components of the Stokes vector belonging to a subgroup of three components of the Stokes vector comprising a second component, Q, equal to the, or a function of the, difference of the two optical intensities of the light radiation reflected by the surface portion on the first pair of polarisation states, a third component, U, equal to the, or a function of the, difference of the two optical intensities of the light radiation reflected by the surface portion on the second pair of polarisation states and a fourth component, V, equal to the, or a function of the, difference of the two optical intensities of the light radiation reflected by the surface portion on the third pair of polarisation states, wherein said number M is equal to 1 or 2 or 3; - generating, for said surface portion, a respective control signal representative of each of said values representative of said components of the Stokes vector; - analysing said respective control signal on said surface portion for detecting the possible presence of surface flaws. - lighting with a light radiation at least one portion of the surface of a tyre or semi-finished product to be inspected; - detecting the optical intensity of the light radiation reflected by said surface portion on a number N of pairs of polarisation states belonging to a group of three pairs of polarisation states corresponding to three pairs of points on Poincaré sphere, the three pairs of points being located at the opposite ends of three respective diameters of the Poincaré sphere orthogonal to each other, said number N being equal to 1 or 2 or 3; - calculating, on said surface portion, a number M of values representative of an equivalent number of components of the Stokes vector belonging to a subgroup of three components of the Stokes vector comprising a second component, Q, equal to the, or a function of the, difference of the two optical intensities of the light radiation reflected by the surface portion on the first pair of polarisation states, a third component, U, equal to the, or a function of the, difference of the two optical intensities of the light radiation reflected by the surface portion on the second pair of polarisation states and a fourth component, V, equal to the, or a function of the, difference of the two optical intensities of the light radiation reflected by the surface portion on the third pair of polarisation states, wherein said number M is equal to 1 or 2 or 3; - generating, for said surface portion, a respective control signal representative of each of said values representative of said components of the Stokes vector; - analysing said respective control signal on said surface portion for detecting the possible presence of surface flaws.