Complex sentence: The official reason for this road not being a motorway is hard shoulders being too narrow although the M275 which the M27 junctions with, has no official hard shoulders throughout its entire length.
Split into simpler sentences: The official reason for this section of road not being a continuation of the motorway is the hard shoulders being too narrow. Although the M275 which the M27 junctions with, has no official hard shoulders throughout its entire length.