Theresa May has so far refused to bow to Liberal Democrat calls to give the people a say on whatever Brexit deal she eventually brings back from our European allies.
But next month the people of Witney will have an opportunity to register their verdict on the Conservative government’s shambolic Brexit negotiations, in a by-election caused by David Cameron’s surprise decision to bow out of parliament.
It will also give the electorate their first chance to judge Jeremy Corbyn's re-election as Labour Leader.
For by-elections are what give opposition parties momentum. If Labour was shaping up to mount a serious challenge to the Conservatives in 2020, it is in by-elections such as this that the Official Opposition would at least be looking to cause the government a few scares.
But what is happening on the ground? Even though Labour actually finished ahead of us at the General Election in Witney, the bookies instantly identified the Lib Dems as the only challenger. While the odds on the Liberal Democrats are growing shorter by the day, Labour's are lengthening to a whopping 33/1.
Already a Labour member has approached Liz Leffman, our brilliant candidate, saying they will support Liz. AC Grayling, the academic, is leading a campaign for tactical voting for the Liberal Democrats as the only party who can beat the Tories.
And this, surely, tells a bigger story. Labour has already been wiped out in Scotland and even under Tony Blair made little impression in southern England. What chance does Labour have in key battleground constituencies when its leadership is only a couple of shades of red shy of being Marxist? I really can't see Labour in its current guise ever winning again.
If Europe is the big question of the day, Labour has no answer. It declined to even debate Brexit at its conference while Corbyn and even Chuka Umunna have hauled up the white flag on Britain’s membership of the Single Market.
No wonder decent, moderate Labour folk are tearing their hair out. Theresa May has a perilously small majority; she clearly has no plan to reconcile the twin demands of free trade with Europe and immigration controls; she is pushing the Tories ever further right, looking to bring back selective education and disowning the campaign of her own Brexit ministers for £350m a week extra for the NHS. Indeed, operation after operation is being cancelled due to the Tories starving hospitals of cash. Meanwhile, as unaccompanied child refugees face hunger and abuse barely 20 miles from our shore, Theresa May looks away.
So a decent opposition should not be short of causes in any campaign against this reckless, divisive and uncaring government. But instead of beating up on the Tories, Labour is beating itself up.
That is why progressives should see that their true home is the Liberal Democrats. Within hours of Corbyn being re-elected, hundreds joined us (adding to the near-on 18,000 who joined the Lib Dems in the aftermath of the referendum).
Increasingly people recognise that we are the real opposition to the Conservative Brexit government. They see a Labour party fatally divided, with no plan for the economy and unfit for government.
Instead of beating up on the Tories, Labour is beating itself up (Getty)
Contrast that with the Liberal Democrats. In government we spread opportunity by introducing free early years education, free school meals, the pupil premium (giving extra resources to children from disadvantaged backgrounds), a national apprenticeship scheme, and tax cuts for low-paid workers. We also legalised same-sex marriage, improved mental health funding (pushing the subject to the top of the political agenda) and increased renewable energy.
Any progressive would cheer such a legacy. And anyone who doubted Liberal Democrat influence in government only has to look at how the Conservatives are messing up Britain without the Lib Dems to keep them in order. The Conservatives are ruling in the interests of the few rather than the many, and recklessly gambling with the economy.
We have so much more that we want to do: give the NHS and social care the funding they need; support our schools; and keep Britain at the heart of Europe. But in these great causes we are now alone.
I am not a home-wrecker, but I do want to be a home-provider. If anyone wants to advance the causes of social justice, please join the Liberal Democrats. I want Britain to be open, tolerant and united – do you?
The Rt Hon Tim Farron is leader of the Liberal Democrats. Visit www.libdems.org.uk to find out more about the party