European Union (Withdrawal) (No. 2) Act 2019
The European Union (Withdrawal) (No. 2) Act 2019, informally referred to as the Benn Act, was an act of the Parliament of the United Kingdom that required the Prime Minister of the UK to seek an extension to the Brexit withdrawal date—then scheduled for 31 October 2019—in certain circumstances.
Source: Wikipedia — European Union (Withdrawal) (No. 2) Act 2019 (CC BY-SA 4.0)