Many thanks for your reply and will look into softwood ply as mentioned.
Attached is an image of natural birch plywood from a US supplier (not so good since in the UK) however it does show the grain I am after. Although finding it very difficult to find a similar grade/ product in the UK.
I have had a search on the forum however most people seem to be after a grade of ply with no knots etc.
I on the other hand am look for a grade and variety of 18mm birch plywood which has larger knots, figuring and colour variations in the grain but not with plugs, patches or too many smaller...