Officially, Above Ground Pipes and Fittings are not made to the appropriate drainage British Standard mainly due to the testing requirements and colour coding rules that identifies what is being carried in a buried pipeline. Therefore, a Building Inspector could insist that the Above Ground components laid underground be removed.
However, as the range of 110mm and 160mm Above Ground Soil Pipes and Fittings are made from the same materials and are the same size, they will perform as well as 110mm and 160mm underground drainage components. The main difference between above ground soil and underground drain is that there is a colour fastness stabiliser in the soil range that is not present in the underground drainage range.