Many thanks for all your contributions which have now led me to believe that using 'clear with clear' or 'solid with solid' parts is the best way to go with this kit.
On a more general note I'm sure from other recent Airfix kits that this is not unique in terms of the lack of clarity of the instructoins so I will double check to confirm and then highlight on the General area of the Forum for further discussion and to highlight to Airfix.
In general the current instructions are a major leap forward with colour coded sections, so credit to Airfix for this, but they are still somewhat behind the competition to my mind. 'R' and 'Ed' amongst others do not have this issue as they show a schematic of the sprues and blank/grey out the parts that are not needed for the build which I find really, really helpful given the myriad of parts that now come with 72nd scale aircraft. Oh for the 60's when a kit and instruction the sheet were so much easier to understand!