The dual purpose of the Act was to increase manufacturing capacity within Great Britain itself, and to limit potential competition from the colonies possessing the raw materials.

Bar iron might be carried coastwise or by land from there to Royal Navy dockyards, but otherwise not beyond 10 miles from London.

Conversely, the Act was designed to restrict the colonial manufacture of finished iron products and steel.

Existing works could continue in operation, but no expansion would be possible in the output of: This was a continuation of a long term British policy, beginning with the Navigation Acts, which were designed to direct most American trade to England, and later Great Britain, and to encourage the manufacture of goods for export to the colonies in Britain.

Part of the reason for lax enforcement may be due to the involvement of Colonial Officials in iron works.