Thousands of migrants accused of cheating the student visa system have been allowed to stay in Britain, a report has warned.

Around 56,000 foreign citizens were implicated in a scam to fake English language tests to beat UK border controls, said the National Audit Office (NAO).

The spending watchdog said bogus students had exploited the lax system in a racket run by criminal gangs.

Yet about 7,500 had been given permission to remain in the UK rather than being thrown out – often challenging the decision on human rights grounds.

Thousands of migrants accused of cheating the student visa system have been allowed to stay in the UK. The 7,500 were given permission to stay often after challenging the deportation decision on human rights grounds. (Pictured) Barriers at Gatwick Airport

The NAO said there had been ‘widespread cheating’ in English language tests. Those claiming to be students needed to pass them before they were granted a visa.

However, the NAO also acknowledged that a ‘small proportion’ of innocent people may have been removed from the UK after being embroiled in the fiasco.

Each year, around 100,000 non-EU students get their visas to stay in the UK extended. Since 2011 foreign students have had to prove they can speak English.

The scam involved corrupt invigilators reading out answers or allowing gangs of imposters to sit speaking tests so the candidates could be awarded an English language certificate.

It meant foreigners who could barely speak a word of English were allowed to enter the country illegally. Gangs were charging around £750 for each fake English language test – four times more than the usual £180 cost.

The Home Office was alerted to the scandal involving the Educational Testing Service (ETS), only after it was exposed by a BBC Panorama programme in 2014.

The ETS is the major company that sets the exams but does not appoint the invigilators.

The NAO report said it revealed ‘organised cheating’ in two language test centres run by third parties on behalf of ETS. An investigation by ETS, using voice recognition technology and human listeners to establish who had cheated by having someone else sit their test, identified 97 per cent as ‘suspicious’.

An astonishing 33,663 UK tests, 58 per cent, were classed as ‘invalid’ while another 22,476 results, or 39 per cent, were considered ‘questionable’. The report said 92 per cent of those found to have falsified tests were fluent English speakers – suggesting a stand-in had sat the exam. The Government responded by cancelling thousands of visas. But the watchdog found 7,467 migrants accused of deception were allowed to stay in Britain – despite the fact that some tried to dupe the system.

Of these around 4,000 were granted leave to remain and 2,600 had successfully appealed against immigration decisions, often arguing that removing them would breach their human rights.

That opened the door to British citizenship, allowing them access to a full range of benefits.

After the scandal was exposed, the National Crime Agency was called in to assist the Home Office’s Criminal and Financial Investigation team. The NAO revealed 25 criminals were convicted for their role in the scam, 21 of them being jailed for a total of 70 years. Four offenders are still awaiting sentence, said the report.

Ministers also stripped 75 colleges of the right to admit foreign students.

At least 11,000 people accused of cheating the language tests have left the country – about one in five of all suspicious candidates, said the NAO.

Sir Amyas Morse, head of the NAO, acknowledged cheating had happened on a ‘large scale’.

He said: ‘When the Home Office acted vigorously to exclude individuals and shut down colleges involved in the English language test cheating scandal, we think they should have taken an equally vigorous approach to protecting those who did not cheat but who were still caught up in the process, however small a proportion. This did not happen.’