One of the country's largest exam boards has identified "significant problems" in a recent think-tank report which claimed single sciences have suffered under Labour.
Cambridge Assessment has cast doubts on Science Fiction?, published by right-of-centre think-tank Policy Exchange at the end of last month.
It set out to "debunk" the Government's claims that take-up of science, technology, engineering and maths (Stem) subjects at GCSE has risen. The study claims that the increase is due to the 75,000-strong growth in school population since 1997.
The think-tank, which was founded by Michael Gove before he became shadow schools secretary, said: "The percentage of pupils choosing to study three separate core science subjects at GCSE barely improved from 1997 to 2007."
Science subjects have been a target for Mr Gove, who picked out examples of the "dumbing down" of science in his party conference speech earlier this month. He read out a question that asked pupils which was healthier - a battered sausage or a grilled fish.
The Policy Exchange report added that there should be greater access to separate sciences for GCSE pupils, while suggesting that O-level candidates had regularly taken all three sciences separately.
But while Cambridge Assessment agrees with the "overall drift" of the report's claims that there has been little improvement in science take-up, it said the main reason for the decline in single sciences was the introduction of double science by the Conservatives in 1991.
Responding to the report, Cambridge Assessment said there was a "dramatic decline" in single science GCSE between 1991 and 1997 due to a "systemic switch to double science".
Tim Oates, head of assessment research and development at Cambridge Assessment, said: "It is important to analyse the volume of science education in terms of population, not just the number of entries into a particular subject."
Anna Fazackerley, head of the education unit at Policy Exchange and author of the report, called for a debate on whether or not double science helped to boost science skills.
"Right now there are two big issues for teachers and parents," she said. "First, 75 per cent of students are now being hived off into a single multiple-choice science GCSE, with one fifth of them choosing not to take a second science GCSE."
"Second, the GCSE science curriculum now focuses on scientific literacy and issues in the news, rather than core scientific skills, leaving children without the basic knowledge that they will need for jobs or life."
This is not the first time the think-tank's reports have been called into question. Earlier this year, its study of Building Schools for the Future accused the organisation overseeing the programme of bullying local authorities.
This was vehemently denied by Partnerships for Schools, which labelled it a "laughable accusation and only slightly less laughable than the accuracy and content of the report".
In 2008, Policy Exchange was threatened with legal action after it claimed a British mosque was distributing extremist literature. A BBC Newsnight programme cast doubt over some of the think-tank's evidence, suggesting much of it was "fake".