A fairly recent acquisition that I have just been photographing. It is an unusual thing with some characteristics of the Mk6 and 6A, and many characteristics of other things, including other NP helmets. Most noticeable will be the very typical NP 'horns' at the top rear, the exterior protrusions of the rubber rivets.
One genuine bafflement is the purpose of the fabric strap, which has velcro rectangles on its interior side. Its not obvious to me exactly what it is all for. May be something related to the faceplate, for which there are obvious mountings. (NB every photo I have seen of this helmet has that fabric strap, so it can be assumed to be a factory fitting, perhaps. I dunno, really. That's why I'm asking you...). The faceplate mounting blocks are bolted on, and so hard to get off I gave up. With the right tools maybe...
I should point out that my example does not have its label - the picture is taken from another otherwise identical helmet.
More pics can be seen here - Composite Helmet, Ballistic helmets, Military helmets UNITED KINGDOM, UK HELMETS, BRITISH helmet, Kevlar helmet - scroll down to or 'find' NATIONAL PLASTICS EOD HELMET.