The government watchdog has launched an investigation after an A-level maths paper was allegedly leaked online, just a day before thousands of students were due to sit the exam.

Exam and assessment regulator Ofqual said it was working with Pearson, owner of exam board Edexcel, to “establish the facts” after the C4 maths exam apparently surfaced on the internet.

Students reported seeing the paper for sale online for £200, with the cheats sending over the first question to prove they had it, but demanding the cash before they would reveal the rest.

Ofqual said: “We are aware of the allegations of malpractice or wrongdoing in relation to Edexcel’s C4 maths paper taken today.

Student mental health pollA pupil taking an exam (David Davies/PA)

“We are working with Pearson to establish the facts.

“We recognise the concerns of students, who should continue to prepare for their forthcoming exams as normal.”

The regulator urged anyone with information on the leak to get in contact or contact Pearson in confidence.

Pearson said in a statement on published on Twitter on Friday that it had been made aware of a “limited breach of security” and that it had opened an investigation.

The company added that the police had also been contacted.

The statement said: “We would like to reassure all students that the planned exams next week will continue as scheduled and that we have established processes in place to ensure no students will be advantaged or disadvantaged in any way.”

Furious students took to Twitter to vent their anger at the exam board.

One user posted: “I am actually so angry.

“Some of us gave our all to these exams so we could be proud of the grades we get at the end.

“If they decide to make use re-sit. I’m not doing it. That’s not the solution. @Edexcel do better. #c4.”

Another said: “This is disgusting. It’s totally unfair on the people doing everything they can to get a grade they deserve @Edexcel do something. #c4leaked.”

Hassan Nassar tweeted the exam board saying: “Again. The ones who cheated are the real winners here. We all know you aren’t going to do anything and probably will not respond to any further replies.

“My grades going down the drain and so is my university offer. Thank you, corporate, capitalist s#%*!”

It is not the first time Pearson has been rocked by leaked exam papers, last year it was forced to amend two maths papers at the last minute after reports some students had had access to them in advance.