I have thought about just buying a piece of wood which would be cheaper, but thanks for the input.
I am now thinking of getting a metal line post and finding some brackets that will wrap around it to attach to the side of the fence post.
Do you think i need to heighten the fence post if it is 6 ft high as i have never had a washing line in the garden before, i have bought a clothes prop but i am concerned if it is too low at one end then it wont work?