Shock absorber and spring assembly for a vehicle suspension, comprising: - a shock absorber having a cylinder and a rod which extend along a first axis (z), - a spring plate which is arranged around the cylinder of the shock absorber and is slidable with respect to this along said first axis (z), - a spring, the bottom of which rests on the spring plate, and - an electromechanical adjustment device arranged between the cylinder of the shock absorber and the spring plate for varying in a continuous and controlled manner the vertical position of the lower end of the spring and thus allowing the clearance of the vehicle from the ground to be adjusted, wherein the adjustment device comprises an electric motor adapted to generate a rotary motion and a screw and nut screw motion conversion mechanism (24, 26) adapted to convert the rotary motion generated by the electric motor into a translational motion of the spring plate, wherein said motion conversion mechanism comprises a single screw which extends along a second axis (z') parallel to said first axis (z) and is adapted to be rotated by the electric motor about said second axis (z'), and a single nut screw which meshes with the screw and is connected to the spring plate for conjoint translation therewith, in such a way that, following the activation of the electric motor, the rotary motion transmitted by the electric motor to the screw is converted into translational motion of the nut screw along said second axis (z'), and therefore into translational motion of the spring plate with respect to the cylinder of the shock absorber along said first axis (z), said second axis (z') being spaced from said first axis (z) in such a way that the unit formed by the screw and the nut screw is arranged eccentrically with respect to the cylinder of the shock absorber and to the spring plate; characterised in that said motion conversion mechanism further comprising a mechanism for blocking the rotation of the screw, which blocking mechanism includes a primary disc which is connected to the screw for conjoint rotation therewith, and an auxiliary disc which is fixed in rotation with respect to the screw, said primary and auxiliary discs having respective profiles (50', 52') which mesh with one another, the auxiliary disc being translatable along the second axis (z') from a blocking position in which the profiles (50', 52') of the two primary and auxiliary discs are mutually engaged and the rotation of the screw is prevented, and an unblocking position in which the profiles (50', 52') of the two primary and auxiliary discs prevent mutual engagement and the rotation of the screw is allowed. - a shock absorber having a cylinder and a rod which extend along a first axis (z), - a spring plate which is arranged around the cylinder of the shock absorber and is slidable with respect to this along said first axis (z), - a spring, the bottom of which rests on the spring plate, and - an electromechanical adjustment device arranged between the cylinder of the shock absorber and the spring plate for varying in a continuous and controlled manner the vertical position of the lower end of the spring and thus allowing the clearance of the vehicle from the ground to be adjusted, wherein the adjustment device comprises an electric motor adapted to generate a rotary motion and a screw and nut screw motion conversion mechanism (24, 26) adapted to convert the rotary motion generated by the electric motor into a translational motion of the spring plate, wherein said motion conversion mechanism comprises a single screw which extends along a second axis (z') parallel to said first axis (z) and is adapted to be rotated by the electric motor about said second axis (z'), and a single nut screw which meshes with the screw and is connected to the spring plate for conjoint translation therewith, in such a way that, following the activation of the electric motor, the rotary motion transmitted by the electric motor to the screw is converted into translational motion of the nut screw along said second axis (z'), and therefore into translational motion of the spring plate with respect to the cylinder of the shock absorber along said first axis (z), said second axis (z') being spaced from said first axis (z) in such a way that the unit formed by the screw and the nut screw is arranged eccentrically with respect to the cylinder of the shock absorber and to the spring plate; characterised in that said motion conversion mechanism further comprising a mechanism for blocking the rotation of the screw, which blocking mechanism includes a primary disc which is connected to the screw for conjoint rotation therewith, and an auxiliary disc which is fixed in rotation with respect to the screw, said primary and auxiliary discs having respective profiles (50', 52') which mesh with one another, the auxiliary disc being translatable along the second axis (z') from a blocking position in which the profiles (50', 52') of the two primary and auxiliary discs are mutually engaged and the rotation of the screw is prevented, and an unblocking position in which the profiles (50', 52') of the two primary and auxiliary discs prevent mutual engagement and the rotation of the screw is allowed.