A method of spirally winding a thermoplastic profile in the manufacture of welded plastic tubes and a winding apparatus for manufacturing a spirally wound tube. A thermoplastic profile is received on a plurality of sliding members being arranged in an axial direction of the tube to be manufactured and defining an essentially cylindrically shaped winding surface with a diameter essentially corresponding to the inner diameter of the tube. The profile is directed along a spiral path towards the previous turn of the profile in order to force opposite edges of the profile together for welding. The radial position of the sliding member is adjusted to control the tension in the thermoplastic profile and the force with which it constricts itself around the winding surface as defined by the sliding member.