Home Secretary Theresa May has been criticised by a former colleague for using "unreliable" statistics to call for tougher restrictions on students coming to Britain.
Ex-universities minister David Willetts took aim at Mrs May's suggestion that 96,000 more students were arriving in the country each year than were leaving.
The Home Office is believed to be considering making places on courses contingent on people demonstrating they have significant independent financial means.
In an article for the Sunday Times, Mrs May wrote: "The gap between the number of non-EU students coming to this country and departing each year is 96,000 - half the net migration from beyond the EU."
But Mr Willetts - who left government last year and is soon to join the House of Lords - said the figure was "not a solid basis for policy".
"People who come here to study should study, perhaps do some post study work and then go back to their country," he told BBC Radio 4's Today programme.
"We are selling them a service, we reap a lot of benefits from that, but studying in Britain is not and should not be a means to settlement.
"My disagreement I'm afraid is that the particular figures that were being cited ... for number of students staying on is very unreliable.
"It is a widely disputed and doubted figure and would not be a solid basis for policy."
Mr Willetts said the information came from the International Passenger Survey (IPS), but had been questioned by bodies including the Commons Public Accounts Committee.
"I don't think it is a reasonable indicator. It is based on a survey - by the time you get down to the number of students - of a few hundred students," he said.
The former Tory MP said in some cases people were recorded as students when they arrived but classed as workers when they left.
Other "better and more reliable" research by the Home Office between 2007 and 2012 indicated just 2% of students failed to comply with their visa requirements.
"My view is that the vast majority do leave," he said. "I don't know why she is using these figures, if she is going to rely on them ...
"Of course they are in circulation, but they must not be used as is a basis for policy.
"It is not the case that out of the 150,000 or so overseas non-EU students who come to Britain every year 100,000, two thirds, of them suddenly breach all their visa conditions and stay on for many years.
"There is no reliable evidence that suggests that is actually happening."