David Miliband:

What is the Benn Act and how does it prevent no-deal Brexit?

The Benn Act is named after Hilary Benn, a backbench Labour Member of Parliament, who rallied a parliamentary majority to defeat the government and insists that if the government has not negotiated a deal with the European Union on the three issues: of Northern Ireland, of citizens' rights, and of financial contributions by the 19th of October, then the prime minister is required to write to the European Union requiring or requesting an extension of the Brexit negotiating process from the 31st of October for three months. So, it ensures, this apparently watertight piece of legislation, that the government cannot lead the UK to crash out of the European Union with no deal at all.