This helmet is known as a sallet (from the Italian celata meaning helmet or ambush). It is loosely attributed to a England owing both to elements of its style and to its reputed discovery in the moat of a castle in either Worcestershire or Warwickshire.
It's possible this helmet saw action during the Wars of the Roses but a hole in the crown (now filled in) suggests it was later used as a funerary helm, placed above the tomb of its owner who wished to be remembered for his warrior prowess. Under the helmet a separate piece of armour, a bevor, guarded the neck and lower face. The sallet's visor allows for very limited vision and ventilation meaning helmets were often removed or visors lifted for a breather, sometimes with fatal consequences. At the Battle of Towton in 1461 Lord Dacre was shot and killed after removing his helmet to take a drink.
The headpiece is forged from a single piece of iron meaning there are no seams which might make it weaker. It has a beautiful moulded shape and an aerodynamic plasticity that would be familiar to an Olympic cyclist. If the helmet is English it suggests a very high level of technical sophistication and artistic ability in the country some time before the establishment of the royal armour workshops at Greenwich in the early years of the reign of Henry VIII.