Sift flour, bread improver and salt into a large warmed bowl, then stir in yeast. Make a well in centre and add warm water. Mix flour and water with a wooden spoon, then beat with a hand, adding a little more water or flour if necessary to make a soft dough.
Turn dough onto a floured surface and knead by folding far edge towards you, then pushing it firmly away with heel of hand. Turn dough a little and repeat. Continue kneading for about 5 minutes, until dough is smooth and elastic and springs back when you make a dent with a finger.
Place dough in a clean, warm, oiled bowl and cover with plastic wrap and a tea towel. Leave to rise in a warm, draught-free place for 1-1½ hours (or in a cool place for longer). Test by pushing a finger into dough. If indentation remains, it is ready. Knock back dough by punching with your fist several times, squeezing out any large bubbles. Turn onto a lightly floured surface and knead three or four times.
Preheat oven to 240ºC or 220ºC fan. Lightly oil a 12 x 23cm loaf pan. Pat dough into a round and fold sides under to form a neat oblong. Place in prepared pan. Cover loosely with plastic wrap and a cloth and leave in a warm place until risen to top of pan. Bake for 15 minutes, then turn pan around, reduce heat to 220ºC or 200ºC fan and bake another 20-25 minutes, until golden brown all over and bread sounds hollow when underside is tapped with knuckles.