Len McCluskey - General Secretary, Unite Union, UK

Stephen Sackur speaks to Len McCluskey, leader of Britain's biggest trade union and biggest donor to the Labour party. Theresa May's proposed Brexit deal is hated by many in her Conservative party. It may well be rejected in a parliamentary vote, but the opposition Labour party is riven by division too. A clear majority of Labour members seem to want a second referendum as a pathway to reversing Brexit. But party leader Jeremy Corbyn says Brexit can't be stopped. Could Brexit break the left apart?