Ministers could benefit from a short induction course on the constitution. Theresa May might then have been reminded of what she probably already knows: it is odd to threaten the judiciary in the terms that she just has on immigration. ‘If they don’t [pay heed to non-statutory provisions] then we will have to look at other measures and that could include parliamentary legislation.’

To this, the only appropriate judicial response is an urbane version of ‘Bring it on’.

Judges are the last constituency to feel threatened by passage of a statute - perhaps other than one diminishing their own generous pension rights or other material interests. For judges of all people, legislation is not a threat: it is their lifeblood. May’s real problem is that she faces difficulties which are political not legal. To prove she is tough on immigration, she can ensure that television news carries pictures of angry foreigners held up by the UK Border Agency at Heathrow. However, with the UK’s economy irrevocably stitched into a rapidly globalising world, she has no hope of meeting the government’s pledge of reducing net migration to ‘tens of thousands’ by 2015. A strict immigration policy would crush the City; bankrupt a significant number of universities; cripple industry and even inconvenience internationally-oriented firms of solicitors - all these groups have put up reasoned cases for exemption from a tough regime.

Overall, the home secretary has limited room for manoeuvre. This is why she has found it convenient to come up with the old chestnut of deporting criminals - something on which the Labour government came a bit of a cropper in its time. May chose to focus on the role of article 8 of the European Convention on Human Rights in protecting the private life and families of undesirable foreign offenders at the expense of their deportation. Restricting the use of article 8 does little to reduce numbers. Estimates of its successful use annually vary between 100 (the courts service) and 400 (UK Border Agency Inspectorate). The home secretary promised a vote in parliament to ram home ‘what the public believe’ and persuade judges ‘to take into account what parliament has said’. Interestingly for such a stalwart believer in parliament, May announced her proposals on BBC1’s Andrew Marr Show the day before she told the Commons.

The home secretary has significant problems on the parliamentary front. First, her party has a deal with the Liberal Democrats to save reform of the Human Rights Act until after the next election. Thus, the consultation paper that preceded the announcement noted the creation of the Commission on the Bill of Rights. This has been designed to kick this issue into touch for this parliament. She has no chance of getting Nick Clegg to pre-empt its recommendations by agreeing, say, anything relevant on article 8. In principle, however, there is otherwise no problem with legislation in this area.

Second, article 8 is, in any event, qualified in its drafting so there is even less difficulty. Article 8.2 contains a list of exemptions including national security, public safety and the prevention of crime. The existing legislation in sections 32 and 33 of the UK Borders Act 2007 deals with this by creating a presumption in favour of deportation of a foreign national sentenced to more than a year’s imprisonment except where article 8 is engaged. Provided this principle is maintained, then the UK is perfectly at liberty to specify the detail in domestic legislation. Excluding a few absolute rights such as the prohibition on torture, the European convention provides a framework not a straitjacket.

One of May’s gripes is that UK judges have developed a jurisprudence rather stronger on article 8 protection than the European Court of Human Rights. An example of this would be a House of Lords decision that stopped the deportation to Lebanon of a mother and child because a Lebanese court would have been required to order custody of the child to her father. It is nice to see government ministers giving such support for the European court. If May wants to override this expression of compassion by domestic judges she can do so by any primary legislation that she can get through parliament.

The home secretary is improperly cutting corners in dealing with her political problems. Our constitution, as May reminds us, is distinguished by the concept of parliamentary supremacy. As defined by its great 19th century apologist, Professor AV Dicey, parliament in this context means ‘the King, the House of Lords and the House of Commons’. And parliamentary sovereignty ‘means neither more nor less than this, namely that parliament thus defined has… the right to make or unmake any law whatsoever’. The Human Rights Act carefully complies with Dicey’s observations. Judges may override secondary but not primary legislation if incompatible with the European convention.

A statement from the UK Border Agency suggests that the government will produce its proposals in the form of amendment to the Immigration Rules. These will ‘take effect from 9 July 2012 following a debate in parliament’. A debate in parliament, even if it takes place in both houses, does not equate to legislation passed by both houses. There is not the opportunity for measured scrutiny in carefully ordered phases over time. Any resolution that arises from such a debate does, and should, not have the force of legislation passed in the proper way and will not be protected by the concept of parliamentary sovereignty. If May wants a statute to bind the UK judiciary, she knows perfectly well how to get it. She certainly needs it. To pretend otherwise is, at best, wrong and, at worst, mischievous.

Roger Smith is director of the law reform and human rights organisation Justice