When all else fails, there's always immigration. That is how many people will respond to Theresa May's apparent determination to bounce this perennially toxic issue to the top of the agenda by flagging up ambitious, but probably unworkable, plans to slash the numbers coming into this country through a range of curbs on citizens' rights to bring in non-EU family members and spouses.

The Home Secretary seems positively anxious for a punch-up. Insisting that the right to a family life as interpreted under the European Convention on Human Rights is being abused, and is not an absolute right but requires qualification, she is courting a battle, both with the judges as well as with organisations like the Joint Council for the Welfare of Immigrants. Ms May is making the most of some notorious cases. Some involve foreigners who have been jailed for crimes and have successfully won the right to remain in this country after their release on the grounds that they have family here, citing Article 8 of the Convention, which declares the right to family life absolute.

Those opposed to Ms May's plans – and especially to the one to introduce a financial threshold for would-be non-EU spouses – are right to point out that hard cases usually make bad law. While moves to ease the deportation of immigrants who are a proven danger to the public have merit, the idea that only the well-off should be able to import husbands or wives from outside the EU will strike most people as unfair.

Meanwhile, it is tempting to see a degree of political opportunism in what appears a calculated attempt to ratchet up the temperature on immigration at a time when, as we report today, the Coalition is dropping further and further behind Labour in the polls.

Ms May has been careless with her brief before out of a rush to grab headlines and sound tough, as we saw in the case of the botched deportation of the radical cleric Abu Qatada. In her eagerness to score quick points with the Tory faithful on immigration we must hope that she does not merely inject a good deal of poison into the subject without having much to offer in the form of useful ideas.