There has been a long-running debate[2][3] regarding whether Parliament alone should have the power to declare war and more widely to commit British forces to armed conflict.
However Queen Elizabeth II, acting upon the advice of her government at the time, refused to grant her consent[4] to allow the bill to be debated in Parliament and so it was dropped (Queen's Consent was needed before debate could take place because the bill affected the royal prerogative).
[4] The Constitutional Reform and Governance Act 2010 originally included a section that would have required Parliamentary approval for use of the armed forces, but this was dropped from the bill before royal assent.
In such a case our actual declaration of war on the expiry of the time limit would take the form of notifying the German Embassy that no satisfactory reply having received from the German Government, His Majesty's Government considered that a state of war between the two countries existed as from a certain time.
[6]The following table refers to declarations of war from the Act of Union in 1707 until the creation of the United Kingdom of Great Britain and Ireland in 1801.