This is the biggest general election in a generation. It will define the future of our country and how we are seen abroad. The Conservatives are driving Britain towards a hard and disastrous Brexit, and this election is our chance to change direction.

We have been given the chance but only if we make our voices heard through the ballot box. That is why today I am asking you to join the fight. If you have looked on as this country, and in fact the world, has lurched from bleak to bleaker – Brexit, Trump, Syria – then this is your opportunity to make a difference, to turn the tide and help create a brighter future.

Theresa May has come back from her Easter holidays realising that she has no mandate. That she is driving Britain over a cliff edge without ever asking the British people if she is what they want. I am glad that she has finally come to her senses and has called for an election.

But let us not be fooled. She is not doing this out of the goodness of her heart. She is not doing this because she thinks the people deserve a say – after all, she refuses to back our call to put the final Brexit deal to the people. No, she is cutting and running because she knows that Labour is in crisis. Her iron convictions proved to be malleable when she scented narrow political advantage. She fears that the Conservative election expenses scandal is closing in on her party, threatening to cut her tiny majority even further. She knows that she is pursuing an agenda that no one has ever voted for. Those are her reasons.

But regardless of her reasons, we now have an opportunity that we cannot afford to fritter away.

If you are a progressive, and see the Conservatives as the problem, then the Liberal Democrats have to be part of the solution. No one seriously suspects that Jeremy Corbyn’s Labour party can prevent a Conservative majority. We must not forget, regardless of what he says during the election campaign, that he ordered his Labour MPs to vote with the Conservatives for Brexit – taking Britain out of the single market, and denying a right to remain for EU citizens. For all Corbyn’s placard politics, it is far from clear how Britain would be significantly different under Labour.

If you want to keep Britain in the single market and keep Britain a country that is open, tolerant and united, then this is your chance. We need your vote.

This is an opportunity to stop May in her tracks in her zealous pursuit of a disastrous hard Brexit, to keep Britain in the single market, to have a decent opposition to stand up to a Conservative government moving from crisis to crisis.

Our NHS, our schools, our prisons, our police forces and our military already face a lack of funding, and the Conservatives will have to make even more damaging cuts to vital services as the Brexit squeeze hits. According to one independent forecast, a hard Brexit will cost Britain £200bn over 15 years. That will be paid for in sacked nurses and teachers – in squalid, rundown public services and unemployment: in short, by the people of Britain.

They badly need a voice. It cannot be Labour. Under Corbyn it is anticipated that they will gift the Conservatives a significant number of formerly red seats. Labour won’t make any gains against the Tories.

As for the SNP, we know that they will do anything to achieve independence. Yes, they are pro-EU, but north of the border only the Liberal Democrats are pro a United Kingdom at the heart of Europe.

Our detractors will ask how the Liberal Democrats can be the real opposition, but a lot has changed since the last election. Our party membership now stands at the highest it has been this century – in fact only an hour after May announced the election on 8 June we added another 1,000 recruits.

It is the Liberal Democrats who have won council seats – week in, week out, some in the most surprising places. As Labour and Ukip fall away, we grow stronger. In byelections we have increased our vote-share, eating into a solid Conservative majority in Witney and overturning a Conservative majority in Richmond Park.

In parliament we are sometimes the only voice of opposition as we have held the Conservatives to account not only on Brexit but on the NHS, welfare cuts and grammar schools.

The Liberal Democrats are the only party that can prevent a Conservative government. There are large numbers of Conservative seats where the Lib Dems are the challengers: seats up and down the country where the Tories are looking vulnerable, where constituents will question this brutal, dumb hard Brexit. The only way to stop May winning a majority, the only way to stop a hard Brexit, is by the Lib Dems winning in those seats.