We are in the middle of the most intense political crisis for a generation. And in a few days Boris Johnson could well be handed the keys to No 10. That will make things worse, not better.

Any responsible future prime minister would have spent the past few weeks seeking to find a consensus in parliament for a way forward, building bridges with our European allies rather than Donald Trump, and making the case for unity not division across the country. For Labour, we have also made it clear that whoever becomes prime minister should have the confidence to put their deal, or no deal, back to the people in a public vote.

Boris Johnson and Jeremy Hunt have not been responsible. Instead they have vied in an arms race towards a more and more extreme form of Brexit. Deeper red lines, even more ludicrous promises, but absolutely no coherent or workable plan for the country.

Johnson has boxed himself in. He does not want to work with parliament to break the impasse, he wants to silence it. In a rallying cry to the extreme Brexiteers in his party, he vows to leave the EU on 31 October “do or die”. That means, by Wednesday afternoon, no deal is likely to be official government policy for the first time.

In the absence of honesty from the Conservative party leadership, it is Labour’s duty to spell out the very real consequences of a no-deal Brexit. It is also our duty to take whatever steps are necessary to prevent it.

I will want to work with all those former ministers who want to ensure parliament can stop a disastrous and chaotic exit

There is no such thing as a “managed” no deal. There will be chaos and legal uncertainty. It won’t be Johnson paying the price of a no deal; it will be working people, their families, and communities across the county. Manufacturing and farming will be hard hit, crucial medicines will be unavailable and EU citizens living in the UK will be left in limbo.

The government’s own economic watchdog has warned that crashing out of the EU would tip the economy into recession. I have spent the past three years travelling across the country talking to businesses and all of them have warned me about the dangers of rupturing our trading relationship with the EU overnight.

The consequences for Northern Ireland are unthinkable, too. The risks of a return to a hard border are real and could fracture 30 years of progress made under the Good Friday agreement.

We simply cannot allow this to happen. Parliament must be put on a war footing to stop a no-deal Brexit when the new prime minister enters office. We did so in March and we must do so again.

Every tool in our armoury must be deployed: amending legislation, forcing emergency debates and triggering no-confidence votes. The majority in parliament must act – and that will involve coordinated work across all political parties.

Last week we claimed a significant victory by making it clear that shutting down parliament in the autumn would be not only unconstitutional, but also unlawful.

The significance of the victory was not just that we succeeded in preventing a future prime minister shutting down parliament, but also its size and spirit. To win by a majority of more than 40 demonstrates a bloc vote determined to stop Johnson’s reckless ideas. And as for the spirit of the vote, I was struck by the fact that many Tory MPs seemed relieved rather than reluctant about rebelling – feeling a sense of pride in doing the right thing.

On Tuesday morning, some ministers will sit around the cabinet table for the last time. They know very well the dangers of no deal. They will have been briefed about what it would mean for jobs, the economy, our public services and the union. They will have seen the advice and read the evidence.

After they have resigned this week, I will want to work with all those former ministers who, like me, want to ensure that parliament can stop a disastrous and chaotic exit from the EU.

So, this week will change everything. The national interest will lie in stopping no deal, not defending a reckless and irresponsible prime minister. The majority in parliament share a common goal: to block a disastrous no-deal scenario. I urge that majority to work together – and together we can take a stand that could change the fate of our country.

• Keir Starmer is the shadow Brexit secretary