Strip away differences of tone and timing, and the clearest political dividing line over Brexit boils down to one thing: what will happen if Britain emerges from EU negotiations with an unappealing exit deal?

For the Conservatives and Liberal Democrats, the answer is relatively straightforward. Theresa May believes the government should, in that case, walk away from talks and leave with no deal. The Liberal Democrats believe the British electorate should have a second chance to reconsider their decision to leave.

For Labour, which is walking a tricky tightrope between leave and remain voters, Keir Starmer on Tuesday offered what might appear to be a third option.

The answer, he says, is first of all to make sure we do not get into this situation. Improve the tone of the talks by making unilateral gestures of goodwill such as guaranteeing the rights of EU citizens. Seek to negotiate a change in the immigration rules of the single market, he says, rather than ruling out participation and then trying to recreate its benefits afterwards, as the Tories favour.

If this fails, argues Starmer, the next step would be to give MPs a chance to reject the deal without abandoning the goal of Brexit. A “meaningful” vote in parliament would be one that was held early enough in the process to send negotiators back to the drawing board to try again if their first draft was a mess.

Only then, concedes Labour, might it be necessary to contemplate how Britain could leave without a deal in place. “In the event that all of that fails, we would have to have contingency measures here to deal with a cliff-edge scenario,” said Starmer, in what was the first and perhaps most significant policy speech of the election.

He insists this is light years away from Tory hardliners, who secretly relish the prospect of what some are calling a “clean Brexit”. But is this really a difference of substance, or merely a debate over negotiating tactics?

The government argues that it has to retain the option of “walking away from a bad deal” otherwise EU negotiators would try to construct one. The merest possibility of a second referendum, argue the Tories, would leave Michel Barnier no incentive to give ground on key issues such as trade and the divorce settlement because there would still be a chance of Britain giving up its goal of trying to leave.

“We want the people to decide and that means allowing them to vote to remain if they wish to,” the Lib Dem leader, Tim Farron, told Peston on Sunday, insisting otherwise Theresa May would have a blank cheque to do as she wished regardless of the consequences.

On this key point, Starmer appears closer to the government position, not least because he says an electorate would still not be in an informed position to fully imagine what life would be like after departure. “As a political party you have to make choices,” he said. “We’ve had a decision and we respect that decision.”

Voters looking for differences between Labour and the Conservatives on this central issue of the election will therefore have to study what Starmer says about the negotiating phase rather than what to do when it is over.

It suits both parties to focus, for example, on Starmer’s promise to guarantee EU citizens rights. The Tories claim, with little evidence, that it means he doesn’t care about UK citizens in Europe. Labour argues, perhaps also hyperbolically, the alternative is holding “hostages to ransom”. Either way, a reciprocal deal on all existing citizens seems likely eventually.

Tories will also try to argue that Labour’s desire to stay in the single market shows it does not care about immigration. Yet Starmer was careful to insist that scrapping freedom of movement remained a “red line” for Labour too – just not the only one.

Instead, just like the prime minister, he believes the EU can be persuaded to give up its cherished freedom of movement rules through some kind of special deal on trade with Britain.

“Whether this is best achieved through reformed membership of the single market and customs union, or a bespoke arrangement, is secondary to the outcome,” said Starmer. “What matters is that we retain the benefits.”

For baffled Europeans, still determined to make sure single market access comes with its existing rights and responsibilities, it may sound like a lawyer’s version of Boris Johnson’s wish to have his cake and eat it.