Prime Minister Theresa May sits behind the Speaker, back row, as Baroness Smith of Basildon speaks in the House of Lords The House of Lords will conclude the first stage of a crucial Brexit debate after Theresa May and Boris Johnson ramped up pressure on them not to block or delay Britain’s exit from the European Union. In a highly unusual move on Monday, the Prime Minister sat on the steps in front of the Royal Throne in the Upper Chamber as Lords Leader Baroness Evans of Bowes urged peers not to frustrate the passage of the Brexit Bill.