I think it's a British MK2 Airborne Troops helmet
I dont think they are very common? the condition looks pretty rough , but it does look interesting with the old paint and salty looks
it may have been used by another country, the Israelis also used helmets like these
An Mk2 helmet steel airborne troops. looking at the paint it might be a post war one.
Obviously if it is then would be a lot less in money terms.
Is it stamp marked on the leather linner band should be a date and maker ?