One of the great mysteries of Theresa May when she became Prime Minister was whether she was a left-wing or a right-wing Conservative? She was once a moderniser who urged the Tories to shed their “nasty party” image, and as Home Secretary she fought modern slavery and the unjustified stopping and searching of ethnic minority citizens by the police.

But she was also the leading proponent in Government of repudiating the European Convention on Human Rights and made an anti-immigration speech at Conservative conference that many of her fellow Tories found shocking.

And now, six months on, we are none the wiser.

During the Conservative leadership contest – cut short by Andrea Leadsom’s withdrawal, which propelled Ms May straight to No 10 – she dropped her plan to take Britain out of the European Convention on Human Rights and its court, admitting that there was no majority for such a policy in Parliament. That seemed to be a pragmatic concession to common sense, realising that leaving the European Union is enough of an upheaval without leaving the separate machinery of wider European human rights law. Even though The Independent sees no need for it, most of the Conservative Party could unite behind a cosmetic rewrite of the Human Rights Act (David Cameron’s so-called “British Bill of Rights”) that would still allow Britain to continue to be a signatory to the Convention after Brexit.

This week, however, it has emerged that Ms May intends to put a promise to withdraw from the Convention in the 2020 Tory manifesto. This is a bad idea on three levels.

The 6 most important issues Theresa May needs to address Show all 6 1 /6 The 6 most important issues Theresa May needs to address The 6 most important issues Theresa May needs to address Brexit The big one. Theresa May has spoken publicly three times since declaring her intent to stand in the Tory Leadership race, and each time she has said, ‘Brexit means Brexit.’ It sounds resolute, but it is helpful to her that Brexit is a made up word with no real meaning. She has said there will be ‘no second referendum’ and no re-entry in to the EU via the back door. But she, like the Leave campaign of which she was not a member, has pointedly not said with any precision what she thinks Brexit means Reuters The 6 most important issues Theresa May needs to address General election This is very much one to keep off the to do list. She said last week there would be ‘no general election’ at this time of great instability. But there have already been calls for one from opposition parties. The Fixed Term Parliaments Act of 2010 makes it far more difficult to call a snap general election, a difficulty she will be in no rush to overcome. In the event of a victory for Leadsom, who was not popular with her own parliamentary colleagues, an election might have been required, but May has the overwhelming backing of the parliamentary party Getty The 6 most important issues Theresa May needs to address HS2 Macbeth has been quoted far too much in recent weeks, but it will be up to May to decide whether, with regard to the new high speed train link between London, Birmingham, the East Midlands and the north, ‘returning were as tedious as go o’er.’ Billions have already been spent. But the £55bn it will cost, at a bare minimum, must now be considered against the grim reality of significantly diminished public finances in the short to medium term at least. It is not scheduled to be completed until 2033, by which point it is not completely unreasonable to imagine a massive, driverless car-led transport revolution having rendered it redundant EPA The 6 most important issues Theresa May needs to address Heathrow expansion Or indeed Gatwick expansion. Or Boris Island, though that option is seems as finished as the man himself. The decision on where to expand aviation capacity in the south east has been delayed to the point of becoming a national embarrassment. A final decision was due in autumn. Whatever is decided, there will be vast opprobrium PA The 6 most important issues Theresa May needs to address Trident renewal David Cameron indicated two days ago that there will be a Commons vote on renewing Britain’s nuclear deterrent on July 18th, by which point we now know, Ms May will be Prime Minister. The Labour Party is, to put it mildly, divided on the issue. This will be an early opportunity to maximise their embarrassment, and return to Tory business as usual EPA The 6 most important issues Theresa May needs to address Scottish Independence Nicola Sturgeon and the SNP are in no doubt that the Brexit vote provides the opportunity for a second independence referendum, in which they can emerge victorious. The Scottish Parliament at Holyrood has the authority to call a second referendum, but Ms May and the British Parliament are by no means automatically compelled to accept the result. She could argue it was settled in 2014 AFP/Getty

First, it is legally fraught. As we report today, an attempt to withdraw from the Convention is vulnerable to challenge in the courts, because the right of appeal to the European Court of Human Rights (the one in Strasbourg that is nothing to do with the EU) is a treaty obligation guaranteed in Northern Ireland by the Good Friday Agreement.

Second, it is politically fraught. Even if pulling out of the ECHR were a manifesto pledge, which should ensure it would pass the House of Lords under the Salisbury Convention, it must be possible at the very least that sufficient Tory MPs in the Commons would fail to support it. That would be a bad fight for Ms May to lose.

The reason she cannot rely on her own MPs, even whipped and bound by party policy, is also the third reason it is a bad idea: because it is wrong in principle.

The Independent understands Ms May’s frustrations with the European Convention and the way the court often interprets it. It made it hard for her, when she was Home Secretary, to deport people whose presence here is not, in the standard phrase, “conducive to the public good”, either because some of the evidence against them might have been obtained (in other countries) by torture, or because there is a risk that they might be tortured if returned to their home country.

But that is the whole point of an international law of human rights. It is designed to protect unpopular people even when to do so is inconvenient for political leaders. That is why the European Convention, because it is above the British state, is so important in guaranteeing the rights of both sides in the Northern Ireland settlement.

Ms May came to office espousing some fine rhetoric of fighting the “burning injustice” of discrimination against the poor, non-whites and women. Her record as Home Secretary in trying to disrupt the causes of modern slavery was admirable.