The head of state is the chief public representative of the state. It is also a symbol of the nation-state. The head of gov leads the day-to-day operations of government.
In Britain, the head of state is the queen. The head of gov is the Prime Minister.
In Iran, the head of state is the supreme leader. The head of gov is the President.
In Iran, the supreme leader has the ultimate decision-making authority and is the final interpreter of shar’ia in Iran. The president is primarily responsible for the day-today operations. In Britain, the queen is merely a symbol of national unity and prestige. The monarch’s relationship with the prime minister is mostly informal and diplomatic interaction with limited political implications
In Britain, Parliament is supreme. There is no oversight to parliament and no judicial review. The only check is a vote of no confidence or the government itself removing the Prime Minister
In Iran, the Guardian Council can overturn anything they do on supreme law. There is no overriding the Guardian Council. The GC can overturn any law.
In Britain, the legislative and executive branches fuse into the westminster system. Westminster uses the legislative branch to initiate the policy through the ministers.
In Iran, the guardian council exercises both legislative and executive powers, however, the supreme leader still holds the decisive power