Core Legal Answer & Context: Delegated legislation is 'substantive ultra vires' when the executive, acting as a delegate, exceeds the powers conferred upon it by the enabling (parent) act, or when the delegated legislation violates fundamental rights or other constitutional provisions. It essentially means the delegate has gone beyond the scope or purpose of the authority granted by the legislature.

Relevant Statutes and Sections: The concept is a common law principle rooted in the doctrine of ultra vires (beyond powers). While no specific statute defines 'substantive ultra vires' directly, the scope of delegated power is always defined by the enabling act passed by the legislature.

Important Landmark Cases:

1. Indian Express Newspapers (Bombay) Pvt. Ltd. v. Union of India (1985): The Supreme Court held that delegated legislation can be challenged on grounds of being ultra vires the parent act, unreasonableness, or violation of fundamental rights.
2. Dwarka Prasad Laxmi Narain v. State of U.P. (1954): The Court struck down a delegated order for imposing unreasonable restrictions, finding it went beyond the scope of the enabling act.

Clear Conclusion: Substantive ultra vires ensures that delegated legislation remains within the boundaries set by the legislature and the Constitution, preventing arbitrary or excessive exercise of power by the executive and upholding the rule of law.