Mr Miliband: "National disease of knocking success"

David Miliband hit back at claims that exams are being down-graded, saying the August debate on education resembled "a pantomime, not a discussion".

He said a threefold increase in students getting two passes or more over the past 30 years was a sign of "meritocracy".

Thursday's A-level results are expected to beat last year's record 95.4% pass rate.

Grades 'myth'

In a speech at a summer school for gifted and talented pupils at Imperial College in London on Tuesday, Mr Miliband attacked the annual debate about whether standards are slipping, saying an education revolution was "opening up educational opportunity to middle England for the first time".

The improved results, he said, were due to the hard work of pupils, teachers and governors and the efforts of parents who wanted their children to have more educational opportunities than they had had.

Students on a summer school for gifted children heard the speech

"My contention is not that today's students are born cleverer than their parents, but that schools and teachers are getting better at getting the best out of them."

Mr Miliband argued that those who say standards have fallen believe only an "elite" could succeed and were trying to defend "the old order of things".

The biggest myth of all was that "more will mean worse, that more education for more people will mean lower standards", said Mr Miliband.

And he had this message for those critics: "Stop saying to the children of people who have not gone to university in the past, who live from Plymouth to Redditch to Sunderland, that there is a charmed circle of educational achievement and it has a big 'keep out' sign all around it".

But Mr Miliband acknowledged that standards must be maintained.

Students are working hard to get the grades they deserve Amalie Peacre, Rainham, Kent Your views

"I have no interest in handing out certificates to people who do not deserve them; I have no interest in pretending to young people that they are capable of something when they are clearly are not.

"But rejecting the myth that more means worse does not mean a culture of prizes for all."

A grades on the rise

The number of students getting the equivalent of two A-levels has gone up from 78,000 to 240,000 during the last 30 years.

Last year, 21.6% of entries at A-level were awarded an A grade and the number is expected to be higher this year.

David Thomas, chief executive of the Careers Research Advisory Centre has called for tougher marking by exam boards, describing rising grades as "rather alarming".

But Ellie Johnson Searle, director of the Joint Council for Qualifications, said A-levels remained an international "gold standard".

Around 250,000 students in England, Wales and Northern Ireland will receive their results on Thursday.