Amber Rudd has quit the government and the Conservative party with a blistering resignation letter in which she condemned Boris Johnson’s decision to remove the whip from 21 Conservative MPs as “an assault on democracy and decency”.

The resignation is the culmination of an intense period of public and private political pressure on Rudd. She – along with the Culture Secretary, Nicky Morgan – was ejected from a WhatsApp group of moderate Conservatives when she stayed in the government, and has since Johnson took office been subject to a great deal of private criticism from friends and allies within the Conservative party. She is one of a number of Conservatives who had believed and hoped that Johnson's no deal position was designed to maximise the prospects of a deal - but now believes that a no deal Brexit is the government's real destination.

That it comes at the same time that former Labour MP and Change founder Angela Smith has become the latest MP to defect to the Liberal Democrats adds to that party’s growing sense that Johnson’s leadership, coupled with the Labour party’s shift to the left, present them with an opportunity for a significant breakthrough. While Smith's previous political positions make her a less natural fit within the party than Chuka Umunna and Luciana Berger, her seat is well outside the party's grasp and most activists will see the defection for what is: a further boost to the party's profile.

It’s no coincidence that the Liberal Democrats have chosen to unveil their defectors in the Times, the Evening Standard and now the Sunday Times - papers who have readerships that are rich in liberal, pro-Remain voters who backed a Conservative vote in 2015 and/or 2017. The Liberal Democrats think that they have successfully taken as many votes as they are ever going to get from the Labour party, and in any case, they believe that their list of plausible targets are mostly Conservative-held, partly due to the extensive private polling they commission and the gains they made in the 2019 local elections.. That ranges from traditional Liberal-Conservative battlegrounds to seats where they have never been competitive, such as Cities and Westminster, where they have conducted several private polls and surveys before unveiling Chuka Umunna as their candidate.

In a happy coincidence for the Liberal Democrats, Rudd’s resignation was also announced in the Sunday Times, where it will further reinforce the message that the party wants to send to liberal Conservatives: that the Liberal Democrats are open for business.

The cumulative message, from Rudd herself, from the Liberal Democrats, and indeed from the Conservative government, who have decided that the next election is going to be about Leave voters, is that Remainers should look elsewhere. While Rudd’s resignation on its own is not going to be a vote-mover, the Conservatives are betting increasingly heavily that their decision to go hell for leather to win Labour seats won’t exert an equal or larger price in terms of the Conservative-Liberal Democrat battleground.