Rot had set in at the base of this post, a common problem. The replacement portion was 800mm long a hardwood key was also inserted to prevent any slip on the joint.
I could have also used a stepped Scarf joint which would have had the same effect as the hardwood key. Because the overall height of the porch was 3.5meters I was concerned that there could still be some movement in the post -possibly buckling , so it was decided to add a handrail and spindles at the end of the porch. This prevents potential buckle in the post and also I think finishes the job off nicely.