Immigration officers have been ordered to stop deporting foreign “students” who overstay their visas. Hundreds of thousands of “students” – including many who never had any intention of studying – will now be staying on illegally and have effectively been granted an amnesty.

Students are by far the biggest category for long-term visitors to Britain, with 1.6 million visas handed out in the last five years. No figures are available on overstayers because no checks are made on who leaves Britain.

The memo was written on December 17 by Jonathan Lindley, director of enforcement at the Border and Immigration Agency, which is struggling against a massive budget overspend.

Sent to the agency’s six regional directors, it reveals how the organisation’s chief executive Lin Homer personally intervened to halt one deportation. The note describes a recent rule change which was meant to crack down on student overstayers, making them automatically liable for refusal if they sought a visa extension.

“A proportion of these refusals have led to removal some of which have been enforced. One such case came to Lin Homer’s attention last week, resulting in the removal being cancelled and some critical comments from Lin. I am surprised that any of these cases have come sufficiently high within enforcement teams’ priorities to merit such quick removal action.

“Please instruct your enforcement teams not to proceed with enforcing any student refusal cases unless they are deemed, at at least inspector level, to be a priority due to Harm (a reference to the Home Office system of gauging how harmful it is for an illegal immigrant to remain in the country).

“Student case working teams have been instructed not to pass any further student refusal cases linked to this issue to enforcement teams.”

Huge numbers of students flock to Britain with 309,000 arriving in 2006, up nine per cent in a year, and more than double the number of foreigners granted work permits.

The personal intervention of Miss Homer, the £200,000-a-year head of the immigration system, to stop an illegal over-stayer from being deported raises grave questions over political interference in the work of frontline staff.