1. Federal form of government must have a Constitution.But, unitary government may or may not have a Constitution.Britain has a unitary government without Constitution whereas France has a unitary government with constitution.
2.Incase of disputes between the institutions of the government regarding the passing of the bill in the Parliament, the judiciary can interfere in the matter to settle disputes. But, incase of the unitary government, judiciary cannot give any judgement on the bill passed by the Parliament.