Create a box pleat down the centre of the pocket piece by folding the pocket in half with the right sides on the inside. Then sew along the stitching lines to fix the pleat lines in place. I stitched down 6cm from the top edge and 6cm up from the bottom edge. This allows the pleat to open as the pocket is being used but won’t distort it out of shape.
Open out the ‘box’ part of the pleat and centre it over the sewn pleat lines. Press the pleat in place.
Fold under 1cm across the top edge of the pocket, then fold the top edge under again along the fold line, this creates the pocket facing. Topstitch along the bottom of the facing to secure it in place.
Press under the 1cm seam allowance along the three remaining sides of the pocket. This will act as a guide later.
Fold the pocket with the right sides touching to pinch together the bottom corners. Sew across the corners using a 1cm seam allowance. Trim off the excess fabric from the corners and turn the right way round.
Fold the seam allowance under the sides and base of the pocket and press in place to create a crease that runs around the front of the pocket. Edge stitch along each of these creases, stopping at the corners and starting again once the corner has been turned.