The writer, a barrister and former Conservative MP, was attorney-general 2010-14

The political challenges the government faces from the arrival of asylum seekers in the UK require some sympathy. Sections of the public are anxious about the numbers and about the difficulties in removing to their home countries those who do not qualify for refugee status. The tragedy in the Mediterranean of a capsized boat from Libya filled with migrants should be a call for more international action, but may fuel yet more insularity instead.

The legislation before parliament, if it becomes law in its present form, will in effect extinguish the right to seek asylum lawfully in the UK. This would tear holes in the international protection regime for refugees — protections we helped create in the wake of the second world war and the Holocaust, and which we are pledged to uphold.

It is, of course, possible to exit such obligations on notice and forfeit our role in helping refugees — something in which the nation has long taken pride. But to claim to adhere to a treaty obligation while trying to evade it is a flagrant breach of the international rules-based system, which our governments constantly say we seek to promote.

Those attempted evasions are pretty stark. All respectable legal opinion agrees that key aspects of the illegal migration bill appear to be incompatible with our obligations under the Refugee Convention, the European Convention on Human Rights, the European Convention on Action Against Trafficking and the Convention on the Rights of the Child. The UK is signed up to all of them.

Blocking access to asylum in the UK without any adequate guarantee that it will be made accessible elsewhere could lead to torture survivors being sent back to the very torturers from whom they fled, as organisations such as Freedom from Torture have warned. Other examples of flouting our international obligations include: denying those who may have been trafficked the support and protection we have committed to, and giving the home secretary discretionary powers to make regulations allowing for the removal of unaccompanied children.

Not only does the bill potentially violate international law; it seeks to alter our domestic law to curtail and undermine the constitutional role of British courts as an independent check on executive action. It is no surprise that the government’s own lawyers have had to advise that the bill could not be published with the usual certificate of compatibility with the European Convention on Human Rights. Yet the government has itself recently acknowledged, in (correctly) binning its flawed Bill of Rights, which was intended to replace the Human Rights Act, that violating or withdrawing from the convention is not an option for us as a civilised state.

In the course of the passage of the illegal migration bill, numerous voices have been raised against it. Theresa May as a former prime minister has expressed her disquiet at the potential impact, particularly on victims of human trafficking. Lord Richard Dannatt, a former head of the army, has said that it “will diminish Britain’s standing in the world”. This month, another critical stage in its passage through the House of Lords provides a chance to uphold those principles of international law that current ministers claim to respect but seem willing to ignore.

There is a broader conclusion to draw here. This bill’s very existence demonstrates that we still appear to be incapable of a reasoned discussion on difficult subjects of this kind. Political rhetoric and posturing leads to poorly drafted, damaging legislation that looks unfit even for its intended purpose. Meanwhile, the courses of action that might make a positive difference — international co-operation in addressing the increase in asylum seekers and increased effectiveness in processing their asylum applications — are, as usual, not deemed enticing enough to be promoted by harried ministers with one eye on the headlines.