The shortage of teachers in Britain's schools is probably higher than 10,000, the shadow education secretary has said.

In an exclusive interview with ePolitix.com, Theresa May warned that "there is a real crisis of teacher shortages" and accused the government of underestimating the number of vacant posts.

Asked about the number of teachers that the education system required, May said it was difficult to estimate the real figure.

"The Times Educational Supplement came up with a survey recently with the figure of 10,000 teacher vacancies. The official government figures are lower than that but government figures have a very strict definition of what a teacher vacancy is. For example, if a school fills a post for a term with a supply teacher, then it isn't counted as a vacancy although they don't have a permanent teacher in post," said May.

May added: "Whether the figure is 10,000 or higher is difficult to say, but certainly there is a real crisis with teacher shortages and I suspect the figure is probably higher than 10,000."

There are a number of solutions, said May, including recruiting more teachers, retaining existing teachers, cutting down on bureaucracy and trusting the professional judgement of teachers.

May also held out the prospect that the Conservative's "free schools" policy could see a return to grammar schools.

"We could very well see some new grammar schools being created but they could also decide to select on a geographical criteria, if for example they wanted to be a community school, or faith based and church schools will be able to select on the basis of interviewing parents which they were able to do until Labour took that right away from them in 1998," she said.

Local Education Authorities would also have a much reduced role under a Conservative administration, said May, as cash would be given directly to individual schools.

May also acknowledged that universities faced a funding problem and said Conservative plans would see the funds available for university endowments gradually being built up.

The shadow education secretary also said the Conservatives would not put a figure on how much it would cost to endow all universities.

"We haven't put a figure on this because it depends on the proposals put forward by the universities. You can't say automatically that a particular grant being received today will be an equivalent of an endowment fund of 'X' million. Of course we have rule of thumb figures that we've been working on but we will wait to see what the universities would propose in the bids they put forward," May told ePolitix.com.