Byelections come in many shapes and sizes. Sometimes they pass without notice. Often the victors are a foregone conclusion. They rarely change the political weather of the nation, notwithstanding the hype. About the only consistent trait is the fevered enthusiasm with which Lib Dems participate in every byelection available. Ignored, derided or outgunned by our larger opponents on the national stage, byelections give us a precious electoral Petri dish in which we can finally compete on a level playing field.

In Witney, thousands of Lib-Dem activists will descend on David Cameron’s constituency to challenge his 25,000-vote majority. Liz Leffman, our superb parliamentary candidate – a local councillor and successful businesswoman – has been omnipresent. Lib-Dem leaflets have rained down on unsuspecting doormats across the length and breadth of the constituency. Inevitably, our exertions are somewhat patronisingly portrayed as the frenetic response of a party still reeling from the drubbing meted out to us in the general election last year.

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But maybe – just maybe – something else is going on. When I visited a farm in Witney recently I was struck how, as we stood in lush Oxfordshire pastures admiring a herd of cattle grazing in near perfect bucolic harmony, the fearful prospect of a “hard” Brexit dominated the conversation. I didn’t ask, but my strong impression was that the family I was visiting had never contemplated voting anything other than Conservative in the past. Indeed, the national status and personable charm of their outgoing MP would have retained an irresistible appeal for such farming voters.

But their unease at what is happening to our country – and what may happen to their family farm – was palpable. What will happen to rural subsidies? Will farm exports be checked at the border? What effect will the plummeting pound have on the price of fertilisers? Why is the government still not providing answers to even the most elementary questions?

These anxious queries are repeated in myriad ways across a constituency that mixes traditional farming with hi-tech startups and a world-beating Formula One industrial cluster. A majority of local voters might traditionally vote Conservative, but a majority voted for remain on 23 June too. And they have been telling Lib-Dem canvassers in growing numbers that they do not want to be railroaded towards an economically self-harming “hard Brexit” by Liam Fox, Boris Johnson and David Davis. They are desperate to see a sensible, balanced approach to our future outside the EU. They are increasingly dismayed by the needless turbulence created by a Conservative party that appears – once again – more intent on talking to itself rather than serving the long-term interests of the country.

Facebook Twitter Pinterest ‘I would urge any Green, Labour and moderate Conservative voter in Witney to set aside their traditional party loyalties and support Liz Leffman.’ Photograph: Tom Pilston/The Guardian

Could this carry Liz Leffman across the winning line? Unlikely – if not wholly impossible, as there is no other candidate from any other party remotely near challenging the Conservatives. Not only would it represent a Lazarus-like resurrection for the Lib Dems, the likes of which we haven’t seen in a generation, it would also require a spectacularly sudden and wholesale collapse of support for the Conservatives. Such sudden abandonment of political parties in government tends only to happen when people are directly feeling the detrimental economic effects of their policies – that may well happen in the next few years, but at present it is an anticipated fear rather than a lived reality for many people in Witney.

But even if such a dramatic upset does not occur today, a strong challenge to Conservative hegemony by the Lib Dems in Witney could nonetheless send a powerful message straight to Theresa May: don’t take your own people for granted, they don’t like the unyielding manner in which you appear to have interpreted the referendum vote; don’t throw the single market baby out with the EU bathwater, the value of people’s jobs and livelihoods cannot be entirely subjugated to the issue of immigration; you may be politically insulated from any meaningful political accountability by a phalanx of aggressive support in the Brexit press, but remember it’s voters not newspaper editors to whom you are ultimately answerable.

So I would urge any Green, Labour and moderate Conservative voter in Witney to set aside their traditional party loyalties and support Liz Leffman as the only candidate able to challenge the hard Brexit-supporting Conservative candidate. I realise I may not be the most obvious person to appeal to Labour voters but we all now operate in an entirely altered political environment. The livid anger of the coalition years between Labour and the Lib Dems – the former condemning every compromise as a betrayal, the latter every denunciation as a denial of economic reality – has now been supplanted by a huge chasm between openness and introversion where we broadly find ourselves on the same side in favour of openness.

British politics is hugely fluid and unpredictable right now. We have a prime minister without a mandate of her own presiding over a hardline Brexit government that is ignoring the deep fractures in a country crying out for more unity, not further division. A vote for Liz Leffman today in Witney could help to tip the balance back to greater reason and moderation.