This is a British MK6 Kevlar helmet, formerly used by the British Army. It does not include the liner, chin strap, or helmet cover. There is an internal marking indicating it was manufactured in 1986, which is said to be from the earliest production run, but I haven't been able to verify this. The size is Large, and it's quite large, suitable for a head size of 60cm. There are no cracks or damage, but there is some paint wear as shown in the images, and there are traces of Velcro stickers inside. If you would like additional images or have any questions, please ask in the comments.