Guto Harri, the former Number 10 director of communications under Boris Johnson, has said it is a "realistic prospect" the Conservatives could move against Rishi Sunak if the results of the local elections are bad.
"I think that would be mad and unfair, but I think it's a realistic prospect now," he tells Sophy Ridge.
"It's clear that one or two mayoral contests could be read as the trigger. It could be that the overall number is so bad that that is the trigger."
'It can be very brutal'
Mr Harri says that, by Sunday, there could be conversations across Westminster on whether Tory MPs could move against Mr Sunak.
"It can happen very, very quickly, and it can be very brutal," noting the speed at which his old boss Mr Johnson was toppled.
Andrew Fisher, former head of policy for Jeremy Corbyn, says that, in contrast, Thursday could be a good night for Labour.
"It's clearly going to be a bad night for Rishi Sunak," he says.