The Green Party hope they can use a by-election to pressure Andy Burnham into committing to electoral reform if he becomes Labour leader in the future.
A potentially final dump of "Mandelson files" is expected next week, piling more pressure on Sir Keir Starmer as he battles to survive as prime minister.
Sir Keir Starmer is due to meet with mooted leadership rival Wes Streeting in Downing Street this morning - just hours before the government's agenda for the coming year is laid out in the King's Speech.
Wes Streeting couldn't have been plotting a coup against Sir Keir Starmer, his friends claim, because he went to the cinema to watch the Devil Wears Prada 2.