Seven years ago, it took just eight words to electrify the Labour conference and to show the party was falling out of love with its then leader. Although not exactly the kind of soaring oratory that gets reproduced on T-shirts, the words were greeted with wild cheering as most of the hall rose in spontaneous acclamation.

As the commotion died down, Keir Starmer, then Brexit spokesman, stood at the podium, blinking in surprise. He wasn’t really accustomed to his speeches having such an effect. All he had said was: “Nobody is ruling out remain as an option.” But context is everything.

During that darkly divisive time of 2018, departing from his agreed text in this way was always going to be seen as laying down the gauntlet to Jeremy Corbyn, who was trying to prioritise leave supporters in working-class seats over the pro-European instincts of his party. In just one speech, this grey-suited shadow Brexit secretary was transformed – if only for a while – into a risk-taker who would stand up for most Labour MPs, members and voters against a leader he would later replace.

Since then, much has happened, not least to Starmer himself. One of his first acts after taking over from Corbyn in 2020 was to declare the Brexit issue had been settled by the previous year’s general election. And, at the last one, he repeatedly emphasised manifesto “red line” commitments that forbade re-entry into the EU, the single market or a customs union. Like his predecessor, his strategy has been to pursue Brexit-y voters in key seats, even if polling evidence suggests many of them have died or changed their minds.

However, it’s now the prime minister’s turn to be an embattled Labour leader. And, if Europe is no longer the boiling pot of British politics, a lid that has been kept tightly sealed for five years is beginning to rattle once more.

Both Starmer and Rachel Reeves have ramped up the rhetoric about the devastation that leaving the EU has caused to the UK’s economy. It’s a useful stick with which to beat Nigel Farage, who now rarely mentions how leaving the EU was once his singular purpose and is still his only real achievement.

And yet the scale of the damage, which by some estimates has left Britain with an economy that is between 6% and 8% smaller than if it were still in the EU, towers over the micro-mitigation so far offered by the government. Starmer’s so-called re-set deal agreed with Brussels last summer offers economic benefits measured in low decimal points. And even while the prime minister hints he would like to do more, it’s far from clear what that means in practice.

The chancellor is among those trying to overcome entrenched Home Office resistance to an expansive version of a growth-enabling youth mobility scheme by which young people can move between the UK and the EU to study or work. The deputy prime minister David Lammy muses openly about the “self-evident” benefits of being in a customs union with the EU, while a dozen Labour MPs, including the chair of the Treasury select committee, last week voted for a Liberal Democrat motion on joining one.

Although Nick Thomas-Symonds , the minister in charge of EU policy, who is now attending every cabinet meeting, insists the red lines are still in place, there are ways these could be bypassed. One idea would be to announce the start of negotiations now on a much bolder deal, for inclusion in the next manifesto, with implementation only if Labour won a fresh mandate.

Yet Starmer has most recently been damping it all down again by warning that a return to a European customs area would “unravel” the trade pacts with the US, which he regards as signature achievements of his premiership.

My understanding is that the PM’s scepticism goes still deeper, and is rooted in three further factors. First, he thinks any customs union agreement has been made significantly more difficult because his ministers are busily de-aligning from European rules across a range of policy areas, including the environment. Second, the exorbitant price set for the UK to join the EU’s new defence fund and the subsequent collapse in talks has convinced UK negotiators that former EU partners are less interested in cutting special deals with Britain than in demonstrating that Brexit does not work. Lastly, the new US national security strategy is seen by some influential figures in Downing Street as a reason for Britain to keep its distance from the EU.

In case you missed it, this bizarre and terrifying document, which has been welcomed by the Kremlin, claims Europe faces “civilizational erasure” because of Muslim migration. Instead of proclaiming our special relationship, it contains only one reference to Britain, which can be found on the same page as a suggestion that Donald Trump’s administration will intervene in our politics to encourage the growth of “patriotic” parties. But, far from concluding that this makes the US an unreliable partner, I’m told the government is worried that aligning closer with Europe would destabilise geopolitics further by risking fragile US military support for Ukraine, Nato and much more besides.

It remains to be seen whether this position can hold if Trump really does seek to export Maga ideology to Britain at a time when Starmer has promised Labour will throw “everything we have” into the fight against rightwing populism. And perhaps, says one source close to him, a more reasonable US president will be in the White House by the time of the next general election. Given the febrile state of Westminster politics, it must be acknowledged there might be a new Labour prime minister too.

All of which brings us back to 2018. Starmer has always said his speech to the party conference was not a pitch for the leadership but merely an attempt to keep open the “option” of remain being on the ballot paper in a new referendum that he was far from convinced was the right solution. Indeed, in those days, Starmer still favoured a “bespoke customs union deal” of the kind he now appears to be opposing.

But it’s not been lost on Downing Street that Wes Streeting, who just about everyone assumes would be a candidate in any leadership election, is among a clutch of cabinet ministers letting it be known they want to go further on Europe. Aides to Angela Rayner, another probable runner in a contest to replace Starmer, insist she won’t discuss her position on a customs union because it would only “escalate unhelpful speculation”.

The danger is obvious. If Starmer rules out more meaningful steps towards a close relationship with the EU, he allows rivals to occupy the space where the overwhelming majority of Labour MPs, members and voters are to be found.

I happen to be someone who both wants him to survive and believes he can do so in spite of all this overheated speculation. But it would be prudent of him to remember the impact just a few words had for him seven years ago. There are options for a big offer on Europe that the prime minister should not “rule out”; he should prise them open himself, before someone else makes them his – or her – own.