New Delhi: HRD minister Prakash Javadekar on Thursday announced that "culprits" responsible for the CBSE question paper leak "will not be spared" and asserted he "could not sleep last night" but did not refer to the board's decision to do away with multiple sets of questions that could have limited the damage.

Javadekar also chose not to touch upon the culpability of the CBSE and his ministry, which controls the national board.

On Wednesday, All India Parents Association president Ashok Agrawal had demanded the resignation of the HRD minister and CBSE chairperson Anita Karwal over the leak of the Class X mathematics and Class XII economics question papers.

"This is an unfortunate development. I understand the agony of parents and students. I am also a parent. Last night I could not sleep. The culprits responsible for the leak will not be spared," Javadekar told a news conference.

"This incident has put a blot on the reputation of the CBSE. The CBSE had credibility in holding examinations. The Supreme Court entrusted it with the responsibility of holding the NEET (because of its credibility)," the minister said.

The National Entrance-cum-Eligibility Test (NEET) is held to admit students to medical courses. Javadekar did not take further questions.

However, academics questioned the CBSE's decision this year to drop its four-decade-old practice of issuing multiple sets of question papers with largely varying questions in board exams.

This year, the CBSE issued a composite question paper for each subject with varying question sequences, as a result of which the re-exam will have to be conducted across the country and not the sector where the question leak was reported. Parents in Delhi had on Wednesday complained about the leak.

Usha Ram, a former principal of Laxman Public School and ex-member of the CBSE governing body, said the system of multiple sets of question papers was "better".

"Certainly the system of multiple sets of question papers with largely varying questions was a better system. I do not know why it was dropped," she said.

CBSE sources said that till 2017, the board used to have three sets of question papers, one for the Delhi region, another for the other regions of India and the third for abroad.

Around 30 per cent of the questions were common across the papers while 70 per cent were different. Within each set there used to be three sub-sets and each sub-set had some varying questions.

However, the board decided to drop the pattern from 2018. It introduced a homogenous system under which the same questions are asked in several sets with varying sequences. "This homogenous pattern has pros and cons. The good thing is that it overrules the apprehension that students in some regions may be getting easier questions. But it increases the damage potential arising out of a localised leak," a principal said.

Principals and teachers across schools are unhappy that nobody is taking responsibility for the lapses that lead to the leak.

The CBSE has started an internal inquiry. Director, vocational education and training, Biswajit Saha, issued a media release late on Wednesday evening saying the inquiry would also suggest how to secure future exams.

The math and economics question papers for the revised tests will be shared as password-protected files with the examination centres to keep them secret.

The CBSE usually sends the hard copies of the question papers to the exam centres from the regional offices through special transport.

The board has started a dummy exercise for sending the questions online through password-protected files, to be downloaded and printed at the exam centres, two principals said.

"Only the centre superintendent will have the password and he or she will download the file. Printouts will then be taken and distributed among students," a principal said.