One in six maths and ICT teachers working today would fail to make it into the classroom under reforms proposed by the Conservatives.
The statistic emerged following the launch of the party's education manifesto earlier this week, which outlined plans to prevent anyone with a degree lower than a 2:2 from entering the profession.
It is estimated that the measures would have barred more than 10,000 teachers currently working in schools up and down the country if they were to apply for teacher training under these rules.
Announcing his party's plans, Conservative leader David Cameron said the Tories would be "brazenly elitist" when it came to admissions to the profession, following the lead set by countries such as Finland and South Korea.
Although many critics have claimed the policy would have little impact as only 4 per cent of teachers currently have a third-class degree or lower, when it comes to shortage subjects - such as maths - the number who would fail to make the grade suddenly jumps.
By raising entry standards, the Conservatives argue that the status of the profession will rise, thereby attracting more, and higher quality, applicants.
Mr Cameron said: "(Countries such as Finland and South Korea) have the most highly qualified teachers, and also some of the best education systems in the world, because they have deliberately made teaching a high- prestige profession.
"They are brazenly elitist - making sure only the top graduates can apply. We should be equally bold here. So we will end the current system where people with third class degrees can get taxpayers' money to enter postgraduate teacher training. With our plans, if you want to become a teacher - and get funding for it - you need a 2:2 or higher."
But James Rogers, executive director of the Universities' Council for the Education of Teachers, said the Conservatives needed to be "very careful" when it came to shortage subjects.
"At the moment, everything is quite rosy," Mr Rogers said. "The recruitment targets are being met (due to the current job market) but the Conservatives will have to be very careful of the possible impact of these measures because the current trend will not last forever.
"We welcome the aspiration of raising the threshold, and our members are already raising the bar to reflect the market, but they will have to look very, very carefully at the detail. They will have to consider certain exemptions when it comes to subjects like maths."
In light of the surge of applicants due to the recession, the Training and Development Agency for Schools (TDA) announced that it would be slashing its "golden hellos" for various subjects, which could act as an additional deterrent to potential trainee teachers once the job market picks up.
The Liberal Democrats warned that the Tories' measures could open the door to staff shortages in schools. Lib Dem education spokesman David Laws said: "Their proposals will mean fewer teachers and even larger class sizes."