Later today the Commons will vote on the Lords’ amendments to the Article 50 bill. One of these amendments concerns the rights of EU citizens currently residing in the UK, after we leave the EU. Over the weekend, in separate interviews, Cabinet ministers Liam Fox and David Davis indicated that a formal agreement on the rights of EU citizens may not come until the final Brexit deal is passed – presumably in 2019.

The government has got itself into an absurd self-defeating mess on the rights of EU citizens, which made it vulnerable to the Lords’ amendment. During the referendum campaign, Vote Leave said that, in the event Leave won, the UK government should guarantee the right of EU citizens who were here on June 23rd to remain and work indefinitely. The same position was subsequently adopted by Nigel Farage. In opinion polls, 84 per cent of Britons, including 77 per cent of Leave voters and 85 per cent of Conservative voters, say that EU citizens should be allowed to stay. Bear those statistics in mind any time, on this issue, someone tells you (as they frequently tell me) that the government’s position is difficult because people voted leave in order to kick EU citizens out.

The government’s position is that it wants to allow EU citizens to stay but cannot guarantee to do so unless the EU correspondingly guarantees to allow the 1.2 million UK citizens who live elsewhere in the EU their rights to stay where they are. This position is simultaneously incredible, offensive, monstrous and absurd.

It is incredible because no-one believes that the UK would deport 3 million people. So the threat to deport EU citizens unless the rights of UK citizens are guaranteed is entirely empty. Even if – contrary to all reason or likelihood – UK citizens had all their property stripped and were force-marched naked to the Channel and sent across in open dinghies, we still wouldn’t deport 3 million EU citizens. We will not deport them under any circumstances, so pretending we might has no credibility whatever.

It is offensive because it implies that other EU countries might consider deporting UK citizens living there. No EU country has said it is considering doing that, there is no reason to believe they might, and given certain aspects of history, suggesting to other EU countries that they might consider mass deportation of foreigners is grossly insensitive.

It is monstrous because, even though there is no possibility of the UK deporting 3 million people, refusing to undertake not to deport them has a material impact on their lives. Some of them may not be sufficiently savvy to grasp that the threat to deport them is entirely empty – they might be genuinely scared. Others may find it difficult to make plans in life over issues like getting married. Some may feel they cannot commit to long-term careers if they are not certain they will be allowed to stay in the UK. Others may fear they cannot secure a mortgage if their residence status is not certain. Holding the threat of deportation over 3 million people – potentially now for nearly 3 years, if no agreement is to be done until 2019 – will have concrete negative impacts on their lives. How ministers cannot see that is extraordinary.

Finally, it is absurd because the government’s position seems to arise from inventing difficulties where there are none. We need to separate two things. First, there is what will happen. Second, there is what won’t happen. Those are two things, not one.

What will happen is complex and detailed and requires negotiation and may well not be settled until late in the Brexit negotiations. After Brexit, will EU citizens in the UK or UK citizens living elsewhere in the EU still be eligible for benefits or tax reliefs? If folk are students, what sort of financial support or access to subsidized accommodation will they be entitled to? If folk are convicted of minor crimes such as shoplifting, will they be permitted to remain or will that lead to deportation? What precise cut-off date will there be after which entry to the UK or the EU will no longer guarantee a right to reside and work? Will foreign citizens be entitled to vote in local elections? And many other complex matters. The government probably should not offer detailed legal undertakings unilaterally over these matters. The best position to adopt on them should to some extent reflect how other EU states treat UK citizens there.

Bu what won’t happen is not simply the obverse of what will happen. The government could, very straightforwardly and entirely within its own power offer political guarantees regarding certain things that won’t happen. In particular, every date the UK government is considering, after which EU citizens who arrive in the UK will not be guaranteed a right to remain after Brexit, is after June 23rd 2016. There are a number of candidate dates. The date could be Brexit day itself. It could be later than Brexit if, for example, we decided to stay in the European Economic Area for a few months post-Brexit as part of the transition process. It could be earlier than Brexit day – e.g. it could be Article 50 triggering day. What precise day we pick might well be a matter for negotiation. But we do not need any negotiation to say that, whatever day it will be, it will be after 23rd June 2016. The government could very simply make a statement to that effect.

Again, there may be some minor complexity over whether we might want to be able to expel people who have been convicted of certain crimes. Fine. In that case, we can make the political commitment to be as follows. The UK will be ending free movement of persons with the EU at some point. We guarantee that, whatever cutoff date is in due course adopted, after which EU citizens entering the UK (and not committing crimes) will not have the same rights to indefinite leave to remain and indefinite rights to work, that cutoff date will be no earlier than 23 June 2016.

This is not a guarantee about benefits or voting or exactly what criminals are or are not allowed to stay or about exactly what cut-off date will apply. All of those can be matters of negotiation. This is, instead, a guarantee that the UK government has it fully in its power to make, unilaterally, because it is a guarantee wholly about the policy that the UK government itself will adopt. It is not a guarantee that no individual will be deported. Bureaucrats could make errors, individuals could commit crimes that lead to their deportation, and various other complicated scenarios. None of that is relevant to this commitment. This is a commitment wholly about UK policy and thus wholly within the power of UK policymakers to give.

We should do it. We should do it unilaterally. We should already have done it. The government’s stubborn refusal on this point is a black mark on Britain’s ethical history.