From distant China, Theresa May has opened a new front against the EU. The Prime Minister has insisted that European nationals arriving during the post-Brexit transition period will not have the same rights as those who arrive before (“I’m clear there is a difference between those who came prior to us leaving and those who will come when they know the UK is leaving.”)

This contradicts the EU's insistence that, in effect, “nothing will change” during the two-year interim phrase (2019-21). Under its plan, European citizens would have the right to stay in the UK, regardless of any immigration restrictions the government later imposes.

May's intervention reflects her personal commitment to reducing net migration and the heat from her party. For the first time in her premiership, May has come under sustained fire from the Brexiteers. Jacob Rees-Mogg, the new chair of the European Reform Group (the guardians of “hard Brexit”), recently warned the UK would be a “vassal state” during the transition.

But, as before, May has picked a battle that she cannot win. In Phase One of the Brexit talks, the UK was forced to accept a £35-39bn divorce bill, European Court of Justice oversight of EU citizens' rights (until 2027) and “full regulatory alignment” in the absence of a new solution to the Irish border problem; what the EU wanted, the EU got. In Phase Two, Brussels will, if anything, be even more stringent in enforcing its rules. Britain cannot expect to maintain the benefits of single market and customs union membership during the transition while simultaneously restricting immigration rights.

As Guy Verhofstadt, the EU parliament's Brexit coordinator, said in response: “Citizens’ rights during the transition is not negotiable. We will not accept that there are two sets of rights for EU citizens. For the transition to work, it must mean a continuation of the existing acquis with no exceptions.” (And the much-maligned EU parliament gets a vote on the final agreement.)

May's approach risks pleasing no one and alienating everyone. Leavers will cry “betrayal” at the inevitable fudge or retreat that follows. Remainers (and EU member states) will be alienated by the Prime Minister's hardline tone. Indeed, May's intervention today will erode some of the goodwill achieved through last December's provisional agreement on citizens' rights.

As the Prime Minister who called an unnecessary election and blew her party's majority, May should know not to pick fights she cannot win. But Brexit shows she has still not learned this lesson.