As the general election campaigns kick off, Theresa May signalled that she intends to recommit herself to the Conservatives’ target to reduce net migration to the “tens of thousands.” It is a target that many – including some of her own colleagues - view as unattainable, undesirable or both. It is no substitute for a policy. And, in contrast to previous elections, where politicians made sweeping pledges, but in practice implemented fairly modest changes to the existing system, Brexit means that radical reform of the UK immigration system is not just possible but inevitable.

The government has refused to say more than it is “looking at a range of options”. Meanwhile, the Labour Party appears hopelessly divided. So here are four key questions for all the parties:

1. What's the point of a migration target?

Essentially scribbled on the back of an envelope, with no serious analysis of either its feasibility or desirability, this target has distorted UK immigration policy since 2010. From either an economic or social point of view, it is almost impossible to justify. If the concern is overall population levels or pressure on public services, then why not target population growth, including births and deaths? (after all, it is children and old people who account for most spending on public services and benefits, not migrant workers). In any case, given the positive fiscal impact of migration, these pressures are mostly a local phenomenon – Scotland is not overcrowded and there is no shortage of school places in Durham. Banning people from moving to London would be much better targeted.

And if the concern is social or cultural – the pace of change – it is bizarre to look at net migration, to include British citizens in the target, and indeed to choose a measure that makes it more attractive to substitute short-term, transient and temporary migrants for permanent ones who are more likely to settle and integrate. Beyond this, there are the practical issues, like the inclusion of students, and the difficulty of managing a target where many of the drivers are not directly under government control. Perhaps most importantly, actually hitting the target would have a substantial economic cost. The Office for Budget Responsibility’s estimates imply that hitting the target by 2021 – towards the end of the next Parliament – would cost about £6bn a year, compared to its current forecasts.

So the first question is, whether the target stays? If so, what are the specific policy measures that will ensure that, in contrast to the past, it is met? And what taxes will be increased, or what public services cut to fill the fiscal gap?

2. How and when will you end free movement?

The government has made clear that Brexit means an end to free movement. Its white paper states:

“We will design our immigration system to ensure that we are able to control the numbers of people who come here from the EU. In future, therefore, the Free Movement Directive will no longer apply and the migration of EU nationals will be subject to UK law.”

But it hasn’t said when this will happen – and it has also stated there is likely to be an “implementation period” for the UK’s future economic and trading relationship with the remaining EU. The EU’s position on this is not hard to guess – if we want to avoid a damaging “cliff edge Brexit”, the easiest and simplest option would be for the UK to adopt, de facto or de jure, some version of the “Norway model”, or membership of the European Economic Area. But that would involve keeping free movement more or less as now (including, for example, the payment of in-work benefits to EU citizens here, since of course David Cameron’s renegotiation is now irrelevant).

So the second question is this – are you committed to ending free movement immediately after Brexit? Or do you accept that it might well be in the UK’s economic interest for it to continue for much or all of the next Parliament?

3. Will we still have a system that gives priority to other Europeans?

During the referendum campaign, Vote Leave argued for a “non-discriminatory” system, under which non-UK nationals seeking to migrate to the UK would be treated the same, regardless of their country of origin (with a few relatively minor exceptions, non-EEA/Swiss nationals all currently face the same rules). And if we are indeed going to leave the single market, the broader economic and political rationale for very different immigration arrangements for EU and non-EU migrants to the UK (and UK migrants to the rest of the EU) will in part disappear. But the Immigration Minister recently said “I hope that the negotiations will result in a bespoke system between ourselves and the European Union.”

So the third question is whether, post-Brexit, our immigration system could and should give preferential access to EU citizens? If so, why?

4. What do you actually mean by reducing "low-skilled" migration?

One issue on which the polling evidence appears clear is that the British public approves of skilled migration – indeed, wants more of it- but not of migration for unskilled jobs. However, as I point out here, most migrants – like most Brits – are neither in high or low skilled jobs. So politicians should not be allowed to get away with saying that they want to reduce low-skilled migration while still attracting the “best and the brightest”.

Do we still want nurses? Teachers? Care workers? Butchers? Plumbers and skilled construction workers? Technicians? If so, do you accept that this means continuing high levels of economic migration? If not, do you accept the negative consequences for business and public services?

Politicians and commentators have been saying for years "you can't talk about immigration" and "we need an honest debate." Now is the time for all the parties to stop waffling and give us some straight answers; and for the public to actually have a choice over what sort of immigration policy – and by implication, what sort of economy and society – we really want.