The breakdown of the Brexit talks yesterday was the latest, but most serious, setback so far. It further eroded the prime minister’s already limited authority. It raised the stakes in Northern Ireland even higher. And it increased the risk of negotiations not progressing to the crucial next phase and a long overdue agreement on transitional arrangements.

Failure to make sufficient progress by next week’s European council meeting would have wide-ranging consequences for jobs, investment and the economy. It’s why I’ve said repeatedly that this is a deadline that can’t be missed. But whatever happens in the coming days, Yesterday’s failure in negotiations brought into sharp focus two underlying flaws in the government’s Brexit approach.

The first is its reliance on the DUP to sustain the government in office. I recognise that for any deal on the Irish border to last, it has to have the support of all communities in Northern Ireland. But it sets a very worrying precedent for the tough decisions to come when the prime minister is called out of a meeting at the 11th hour and told by the DUP that the deal is off. That is a terrible signal to send to the EU about the prime minister’s ability to deliver Brexit. It shows that the DUP now has a veto on any proposal she makes.

The second major flaw in Theresa May’s approach concerns the ideological red lines she set out in her 2016 Tory conference speech, and underlined in a speech at Lancaster House. Those red lines swept the customs union and single market off the table, along with any future role for the European court of justice. This was always an extreme interpretation of the referendum, and was always going to pose significant problems on any number of issues – including the future of the Northern Ireland border. The government’s contortions in recent days ought to be a warning that it is on the wrong track.

Similarly, progress would have been far easier if the prime minister had matched Labour’s clear commitment to seek transitional arrangements on the same basic terms as now – including remaining within a UK-EU customs union and the single market during this period.

This would – as I emphasised when announcing this policy in the summer –have allowed “more time to resolve the complex question of the Northern Ireland border” and to reach a “considered agreement that prevents a hard border and has support from all communities”. Instead, Theresa May has stuck to the same red lines, whatever complications this has inevitably caused.

As I made clear in the Commons today, there needs to be a UK-wide solution to Brexit. So if there is to be regulatory alignment with the EU after Brexit – and I hope there will – it has to be across the whole of the UK, not one part of it. And if the price of the prime minister’s approach is the break-up of the union and the reopening of bitter divides in Northern Ireland, then the price is too high.

Labour would start negotiations with the EU in a fundamentally different place. We have said that remaining in a UK-wide customs union with the EU is a viable option, subject to negotiations. We accept that any lasting and close partnership with the EU will require a court. We are open as to whether the benefits of the single market are best retained by negotiating a new single market relationship or by working up from a bespoke trade deal.

We have a manifesto commitment to ensure there is no hard border in Northern Ireland. This would not make it easy to reach a Brexit deal that works for all nations and regions of the UK. But it would make it easier. And it would provide a basis for the strong future partnership we need with the EU.

There is still time for agreement to be reached before the EU council next week. As someone who passionately believes we need to build a strong future partnership with the EU, and to urgently secure strong transitional arrangements, I hope that is achieved. But the stakes could not be higher. There can be no more failures.

The most effective way forward would be for Theresa May to rethink her reckless red lines and to put options such as a UK customs union with the EU back on the table. If she does not, yesterday’s farcical scenes will merely be a precursor to the rest of the negotiations.

• Keir Starmer is a Labour MP and shadow secretary of state for exiting the EU