Theresa May has outlined her plan for Brexit. The debate over process will doubtless rumble on. However, it is time to start to think about substance. In her Lancaster House speech, the prime minister stressed that Brexit means regaining national control over our laws and our borders. At the same time, however, she expects Brexit to make Britain stronger, fairer and more global.

But how will we know if the government’s plan sets out a coherent strategy for a successful Brexit? How should we judge the terms of any eventual deal and our disengagement from the EU? Over the long term, how will we know if Brexit is really “working for Britain”? In order to answer these questions, we need to move beyond platitudes to focus on likely outcomes for individuals, families, businesses and the country as a whole. We need to know not just what Brexit means, but what constitutes “success” and what “works”.

For this, we need an agreed set of “tests” against which we can evaluate the substantive impact of the process. This is not about rerunning the referendum campaign; it is about assessing the impact of the specific form of Brexit that has been chosen. Consequently, we at The UK in a Changing Europe have come up with what we feel are a set of objective tests capable of reflecting a consensus across the UK – including people from both sides of the referendum debate.

Although the two sides disagreed vehemently about whether we should remain in the EU, there was considerable common ground – reflected in the PM’s speech – about what we, as a country, should be seeking to achieve. Generally, both sides argued that Britain should remain an open, outward-looking country (immigration policy notwithstanding); that both economic growth and social cohesion mattered; that we should invest in, and improve, our public services; and that we needed to preserve – or reassert – control of our own destiny. Any attempt to measure the success of Brexit must reflect this broad range of goals.

So, we have devised four tests that can be applied to the British economy post-Brexit to attempt to elucidate its impact. The first relates to the economy and public finances in general. Will Brexit make the country more prosperous? As the chancellor Philip Hammond put it, nobody voted for (or indeed against) Brexit to make us poorer. A successful Brexit will be one that makes us better-off overall.

Our second test relates to fairness. The referendum campaign crystallised a view that many people had been “left behind” by the relative success of the UK economy since we joined the European Union. A successful Brexit will be one that helps those who have done worst, and promotes opportunity and social mobility for all across the UK, but particularly for the most disadvantaged.

Third, will Brexit preserve and extend the UK’s openness as an economy (to trade, investment, ideas and people)? The prime minister has stressed that a global Britain will be outward-looking, a “great, global trading nation”. The UK has a long and well-established consensus, across the political spectrum, in favour of free trade and open markets as a means to greater prosperity. A successful Brexit will be one that maintains and enhances the UK’s position as an open economy and society.

And finally, will Brexit enhance the democratic control the British people exercise over their own socio-economic destiny? Control is not just about the formal sovereignty of Westminster, but more broadly about whether individuals and communities feel they have a genuine say in the decisions that affect them. A successful Brexit will be one that genuinely increases citizens’ control over their own lives.

We do not have a view on whether the tests are likely to be met, or what Brexit would have to look like to meet them. Rather, we are setting out a framework intended to be, as far as possible, neutral and objective, which will allow for such an assessment in the future. Of course there will be deep and sincere differences on how we achieve them – but we hope that there is a consensus that they are broadly the right objectives.

So how do we test whether those four objectives are deliverable? We have only set out the framework for the tests – we have not sought to specify in detail the necessary measures or indicators, let alone assess whether they are likely to be met. But moving forward, there needs to be some clear, evidence-based and, as far as possible, objective mechanism for assessment. Whatever method is chosen, what is important is that the credibility of both the tests and the process are established in the minds of the public at large.

We are entering a period when the choices we make, collectively, will determine our future for decades – the significance of Brexit to the UK, economically and socially, cannot be overstated. We all have a stake in making a success of Brexit. But to do that we need to have a shared vision of what success means.

• This article was co-authored by Anand Menon, a director of The UK in a Changing Europe