I am currently in dispute with the local Sewerage Undertaker regarding building over a 100mm pitch fibre sewer pipe. The SU insists that I should pay for replacing the pipe with malleable iron. Amonst other things I am arguing that the pitch fibre is nearly 40 yrs old (I have drawings showing the sewer in 1972) and CCTV has proved it to be in poor condition, they should pay for replacement. They are now trying to say that the sewer was laid in 1980 so is not beyond its reasonable life. My experience, and internet searches, show that Pitch Fibre was discontinued in the early 70's. In fact in the midlands we had discontinued PF in the late 60's. The question is: If they stick with their claim that the sewer was laid with PF pipes in 1980, Can I claim that they were not acting with due diligence,as they used a material which has been proven unsuitable?