Richard Burbidge does a very good range of stair newels, spindles and rails, The last set I fitted for a friend of mine was to replace square newels and boarded rails with turned newels and spindles, the old newels were cut off square at the same height as a standard newel base and the centre was marked and drilled with the drill purchased with the new parts. Ask your supplier for the correct one. Then you can chamfer the edges. The new newel post had an integral split tapered turning at the base with a hole through its centre to take the tapered dowel from the underside. The hole in the old newel base needs to be drilled slightly deeper than the length of the turning on the base of the new newel post, the tapered dowel is then cut to length, this is determined by the depth of your hole and the amount the dowel needs to pertrude into the base of the newel post so that when fitted it opens the base of the post enough to fit tight into the hole. Once this has been set up, glue needs to be coated around the turning at the bottom of the newel post and also onto the dowel, the dowel is then placed into the hole in the bottom of the newel post so that it just holds there, then the post is placed into the hole of the newel base and carefully hit down into the hole. when the post comes to near the bottom of the hole, the dowel has already hit bottom and is then forced up into the post so as to open the bottom out forcing it against the newel base. you need to be precise with the measurements or one of 2 things can happen....1) the dowel is too short and does not open the bottom of the post out enough to clamp it in the hole or ...2) the dowel is too long so when the post is hit down the dowel opens the bottom of the post too early not allowing the post to complete its travel into the base. Be careful when fitting the newel to ensure the square top is in line with the base because it will never turn after fitted. You will have to do this for each post replacement. Then it is just the case of fitting the hand rail and spindles as per the instructions so to comply with regulations.