With her first major speech [2] on immigration, Theresa May has begun to spell out how exactly the government plans to bring about a drastic reduction in the number of people settling in the UK.

First, more than 100,000 skilled workers and overseas students who come to Britain each year will lose the right to permanent settlement.

Second, the number of students who come to the UK to study below-degree-level courses – roughly 160,000 each year – will be slashed. They make up nearly half of the total of 320,000 international students, and are apparently more likely to overstay.

Perhaps taking into account that the Commons home affairs committee's Immigration Cap [3] report last week underlined the "crucial importance" of international students to the UK, May stressed that students at degree level or above would not be affected.

Third, she backpedalled on David Cameron's Wednesday announcement that 30,000 migrants working for multinational companies would be exempt from the immigration cap. May said there would be a minimum-salary limit on this of roughly £40,000, to ensure that people are transferred for specialist or managerial positions only.

These measures are the first solid indication of how the government intends to keep its election promise of bringing net migration down into the "tens of thousands" from the current level of 196,000. The recent Commons report was unequivocal in its conclusion that "the proposed cap – unless it is set close to 100 per cent – will have little significant impact on overall immigration levels".

Clamping down on student visas and permanent settlement are the two obvious ways to go about reducing numbers, given that the flagship "immigration cap" policy is essentially unworkable. However, this will not necessarily provide the immediate results that the government needs.

Professor David Metcalf, chair of the Migration Advisory Committee [4], points out that "any such changes [to permanent settlement], even if introduced now, would not take effect until 2013-14".

Analysing the committee's report last week, Alice Sachrajda of IPPR [5] noted that:

The policy of a cap was introduced as an election promise and so a more immediate outcome will be needed if the government is going to save face politically.

. . . It is now abundantly clear that achieving its policy objective of drastically cutting net migration is going to be an uphill struggle for the government. The coalition faces an unpalatable choice between introducing an ineffective policy that it knows is damaging to the economy and public services, or by finding a way to abandon or redefine the target.

The headache caused by the unfeasible and misguided policy of the "cap" is certainly not cured yet. Taken alone, these measures are unlikely to meet the arbitrary target of at least halving net migration. Taking steps to avoid damaging business or reducing university revenue even further, such as allowing intra-company transfers and degree-level students, makes the target even more distant.

More importantly, the government has yet to address the question of top businessmen, scientists and researchers from outside the EU, who still look likely to be the losers from more draconian immigration rules. A Nobel Prize-winning scientist [6] (£) points out in the Times today that he might not have carried out research in Britain had these rules applied in the past – even if he had gained a visa, members of his team might not have done.

The government would be well advised to drop this meaningless target altogether.