As we enter the endgame of Brexit, two countervailing trends dominate our politics. The first is that more and more people have come to see that Brexit is a crisis on a par with any of the great crises in modern British history. And the second is a growing sense – fuelled by those who lurk in the shadows of our embattled prime minister – that there is no time to do anything about this crisis; that we should be focused on “softening” Brexit because there is no time or space to change course. Around the country, at event after event, I hear the same refrain: “maybe we should stop Brexit after all, but can we really do it?”. My answer has always been “yes” and “yes” – we should stop Brexit, we can stop Brexit. But it is important to explain how.

First, we must be clear that the goal must be to stop Brexit entirely. Brexit is a cliff, not a gradient. The mistake we are in danger of making is to believe that some Brexits are better than others when the fundamental problem is Brexit itself.

Being on the edge of a cliff, the necessary course is to step back from the edge, and not delude ourselves with ever more absurd and bizarre schemes for jumping over while clinging to a branch and hoping to find a ledge a third or half the way down. We are at risk of pursuing a Wile E. Coyote Brexit – running so fast over the edge that we don’t notice, until it is too late, that there’s nothing holding us up.

It is now crystal clear that the fatal flaw of Brexit is the act of putting the UK outside the European Union – its markets, its customs union, its institutions, its law, its leadership, its future. Working out what we might do having left is the politics of “least worst” options, unworthy and dangerous for this nation and this people with its European geography and destiny.

After two years of ceaseless Brexiteering by government and parliament, it is a statement of fact that there is no viable Brexit plan on offer, none in sight, and that all of those mooted involve massive dislocation and ongoing uncertainty for our trade, our security, Ireland, and our whole international position as a country. Even if we could get to something like a Norwegian or Swiss option – and don’t get me going on the complexities even of those, and of course such arrangements aren’t remotely government policy – the difference between that and our present position in the EU would have to be measured in miles, not inches. And anything short of this is frankly ludicrous, as the last few weeks of “keep calm and carry on”, Battle of Britain-style planning for food stockpiling and transport chaos has demonstrated.

Point two. The path away from the cliff edge is for Theresa May to announce that the government’s Brexit deal will be put to a referendum after it comes to parliament at the end of the year, giving the people the choice not to proceed and instead to stay in the European Union. If the prime minister will not do this, the House of Commons should direct her or her successor to hold this referendum, as it has directed monarchs and governments in moments of national crisis over the centuries since Magna Carta.

There is a lot being said about democracy and referendum results that must be honoured irrespective of circumstances. Democracy is not a single event; it is a process of constant public engagement, what Clement Attlee called “government by discussion”. That discussion is not over simply because Jacob Rees-Mogg declares it over. The people should make the final decision on Brexit when they see the government’s Brexit deal.

So my second point is to state clearly that a people’s vote – to stop a government potentially harming the people – not only accords with our constitution and traditions, but in my view is necessitated by them. Parliament has, as Gladstone said in respect of self-government for Ireland when he proposed it in 1886: a “golden moment” to resolve an imminent national calamity. True, the moment does not feel especially golden, but nor was it when Gladstone spoke amid continuing Irish terrorism and civil insurrection in parts of Ireland. His point was that parliament had a rare moment of autonomy in the power to act. Which is precisely where we are at the moment with Brexit: we have the autonomy – the privilege indeed – to act now before the timetable to actually leave the EU on 29 March next year overwhelms us and we lose control of events, as we surely will.

Which brings me to point three. Brexit will only be stopped if members of parliament show courage and leadership at this “golden moment”. If, in the historic Brexit votes soon to come, MPs hand their consciences to party whips and leave it to others to do their duty, we will most likely end up in a “blind Brexit” in which we leave Europe next March without a credible plan for our national future, whatever the immediate provisions for stability. For this, we and our children will pay a steadily greater price in economic, diplomatic and possibly security vulnerability until, as we surely will in the next generation, either by our initiative or through European crisis, we once again take our place in the European Union.

So this is the strategy I propose, along with many other parliamentarians and others who have been wrestling with these great issues and with whom I have been in a virtual committee of public safety in recent months.

First: Brexit can and must be stopped, democratically.

Second: this can and should be done by means of a people’s vote.

Third: it is the duty of all MPs who realise that Brexit is wrong to support the people’s vote and give their frank advice to their constituents on the right course to stay in the EU.

It is simple, straightforward, entirely achievable and I believe entirely legitimate. The question now is whether my colleagues in the House of Commons will seize their “golden moment” and act to give the people their say. History tells us that the consequences, should they fail, will be severe. As will be the judgment of history.

• Andrew Adonis is a Labour peer