Saw this for sale at the local hardware store in town: ]
This is sold as 12mm marine ply, has the correct Loyds of London stamp on it to. Maybe BS does not stand for British Standard after all?
Shows that you have to be careful where you purchase your supposedly BS1088 rated wood from!
Fairly certain that ain't marine ply. In my (limited) experience, marine ply has many more layers per??? and the layers are all a uniform thickness.
Seems from your photos that the thicker laminations are just a soft filler ply.
This fellow, Denman Marine seems to know what he is talking about, he is quoted as knowledgeable on many of the woodworking and boat building forums.
It is an interesting read if you are considering purchasing marine ply.
It could also be handy that he is only about 20Km down the road from me!