Brussels, April 11 -- As if Brexit hadn't spooked Britain and the European Union enough over the past three years, the two sides agreed early Thursday to extend the deadline to Halloween.

The new, Oct. 31 cutoff date averts a precipitous and potentially calamitous Brexit that had been scheduled for Friday.

"Please, do not waste this time," European Council President Donald Tusk pleaded. He said the EU was giving Britain six more months "to find the best possible solution" to its Brexit impasse.

Like many things related to Brexit, the extension was a messy compromise. May came to an emergency summit in Brussels seeking to postpone Britain's departure from the EU until June 30. Some European leaders favored a longer extension, while Fren...