Boris Johnson’s premiership has been plunged into further crisis tonight by the resignation of the Brexit minister Lord Frost. Frost has, according to the Mail on Sunday, quitover the political direction of the government, citing Plan B, tax rises and net zero.

His decision to go makes Johnson more vulnerable than he has been at any point in his premiership. He has lost the man who negotiated his Brexit deal, the person he used to reassure hardline Brexiteers he wasn’t going soft and the second most popular member of his Cabinet among the party faithful. Frost, a canny political operator, will know just how much his departure will weaken Johnson, and the reasons he has given for leaving hit the Prime Minister’s weakest spots with his activists. There’s little doubt that it will be seen by a group of Tory MPs as a signal to put letters in.

Frost’s resignation is a body blow to Johnson. Johnson has made much of his Brexit sherpa, he elevated him to the Cabinet – in part to stop him leaving government– put him in charge of relations with EU governments, much to the then-Foreign Secretary Dominic Raab’s chagrin, and repeatedly praised him as the greatest Frost since the Great Frost of 1709. Frost was meant to act as a sign of the government’s resolve on Brexit-related issues. For him to go while negotiations with the EU over the Northern Ireland protocol are ongoing is devastating.

In recent months it has been increasingly clear that Frost was unhappy. He felt that the government was not seizing the opportunities of Brexit. He was clear that if the UK was to leave the single market and the customs union but carry on as before, Brexit would not succeed. In a speech to the Centre for Policy Studies he declared,

‘If, after Brexit, all we do is import the European social model, we will not succeed.

We haven’t successfully rolled back the frontiers of the EU with Brexit, only to import the European model after all this time.

So we need to reform fast and those reforms are going to involve doing things differently from the EU.

If we stick to EU models, but behind our own tariff wall and with a smaller market, obviously we are not going to succeed.’

In Cabinet, he was one of three ministers to speak out against increasing National Insurance to pay for more spending on health and social care. Privately, he was adamant that leaving the EU and then hiking taxes was the wrong thing to do. Publicly, he warned that divergence from EU rules was a ‘national necessity’ if Brexit was to succeed. This raised the question of why there had been so little of it.

Tonight, Boris Johnson faces the greatest crisis since his election victory two years ago. Defeat in North Shropshire and the national polls are chipping away at his standing as an electoral asset and David Frost – a man he elevated to the Lords and the Cabinet – has now taken a hammer to his Brexit credentials. Combine this with the unpalatable decisions that Johnson is facing on Covid and it’s clear that the Prime Minister is now in a very exposed political position.

Below is Lord Frost’s letter to the Prime Minister:

And Boris Johnson’s response: