A former trade union leader and a Conservative prime minister have never before put pen to paper together. We do so today in very special circumstances. With the prospects for working people all across Britain at stake on 23 June, it is right that the rules of conventional politics be temporarily set aside. There are, of course, many things on which the two of us disagree. But we are united in our conviction that Britain, and Britain’s workers, will be better off in a reformed Europe than out on our own.

While staying in Europe offers workers in the UK the best prospects of rising prosperity, leaving poses what we call a triple threat: to working people’s jobs, to their wages and to the prices we all pay in the shops. Let us take each in turn.

First, the risk to jobs. Even some prominent campaigners on the leave side are now agreed on this – leaving the European Union will cause an economic shock. Let’s be clear about what that means: an economic downturn; people losing their jobs and livelihoods; parents left unable to provide for their families. An independent estimate by the accountancy firm PwC states that unemployment could rise to 8% by 2020, compared with just 5% if we stay in the EU.

That’s bad enough, but there would be a longer-term consequence too. As last week’s Treasury analysis showed, Britain’s GDP will be permanently lower than it would otherwise be – around 6% lower by 2030, the equivalent of £4,300 for every household in the country. So let there be no doubt about what leaving the EU means: an immediate shock, and then a permanently poorer country.

That leads us to the second threat: wages. It’s clear there will be long-term damage for our country’s productivity, caused by the second-rate, more restrictive trade relationship we would have to try to negotiate if we left our home market of 500 million consumers. Less open trading leads to lower productivity.

And we must be equally clear about what that means for working people: even if they keep their jobs, their wages will be lower than they would otherwise have been. That would be a disaster for working people, and it will be those industries that rely on exporting to Europe the most – manufacturing and services – that will be hit hardest.

So it doesn’t matter whether you work in a car plant, a factory, a shop or an office: the likelihood is that you would take home less money at the end of every month than if we had stayed in Europe. And let’s not forget that, while the two of us may disagree about quite how far this process should go, being in Europe has helped to deliver many of the crucial rights that underpin fairness at work. Paid holidays, maternity rights, equal treatment for the millions of people working part-time, protections for agency workers, even equal pay for women at work: all are guaranteed by Europe and all could be at risk if we left.

Of course, slower growth will feed through to the public finances too. It would hit our tax revenues, generating less money to pay the wages of public sector workers such as nurses and teachers. So we face a vicious circle that will hurt the lowest-paid workers in every part of our economy – public and private sector alike.

The third threat is rising prices. It’s quite simple: most independent experts agree that leaving Europe would put pressure on the pound. Indeed, we’re seeing that pressure already as fears grow of Britain leaving the EU. A weak pound means more expensive goods and higher inflation, pushing up the prices of the weekly shop, clothes, petrol – anything that we import from other countries. So we are likely to see the cost of living going up, just as wages are being squeezed and jobs lost. That is the threat for families already struggling to make ends meet – and a risk that working people and the poorest in our country simply cannot afford.

So the choice before us is becoming clearer each day. We can risk jobs, hold down wages and pay higher prices. We can be the first major economy in history to deliberately choose a second-rate trading arrangement for our biggest market. We can take needless risks with our economy that would unleash a triple threat to working people – and become a poorer country in every sense.

Or, if we choose to stay in the EU, we can protect working people and the poorest families. We can choose stability and economic security – a bright future with more jobs, higher pay and lower prices.

As you make that choice, remember this: on the leavers’ side there is a real lack of credible experts to support their case. And there is a troubling dogma in their rigid belief that, in the face of all evidence to the contrary, taking these risks will be worth the pain they will cause. The leavers now say they want the UK to be like Albania, which even the Albanian prime minister says is “weird”, because his country wants to be more like us.

On our side, however, we have a collection of independent experts, trustworthy organisations and friends of Britain from around the world. Whether it is the Bank of England, our universities, the trade unions, employers large and small in every part of our economy, the IMF, President Obama, our allies in Nato or the Commonwealth, the message is the same: Britain is better off in Europe.

Of course, the leavers say this must be some sort of conspiracy masterminded by shadowy international elites. All we have to say is: to have been able to bring even the two of us together today, these evil geniuses must be very good.

For the sake of every worker in Britain, we urge you: vote to remain.