Border staff are to be given extra powers to refuse visas to foreign students they suspect are really coming to this country to work, the Government will announce today.

The move comes as ministers search for ways of cutting migrant numbers coming to Britain. They believe that abuse of the student visa system is one of the main back door routes into the country.

At the moment, immigration officers can refuse visas to applicants if they do not speak adequate English or if they are heading to a college that is not recognised by the Government. But their powers are being widened from 30 July to allow them to veto "high-risk applicants" on the grounds they do not genuinely intend to study.

Those suspected of planning to abuse the system will be asked in detail about their educational history, their study and post-study plans and their financial circumstances. The UK Border Agency is expected to carry out up to 14,000 student applicant interviews over the next year.

Under a further change introduced today, an official will also be able to refuse entry to an applicant who fails to attend an interview without providing a reasonable explanation.

The Government has promised to bring net migration numbers down from "hundreds of thousands" to "tens of thousands" by 2015. At the moment the figure remains around 250,000, but ministers insist that changes in the pipeline will soon begin to have a marked effect.