An influential Parliamentary committee will launch a full inquiry into the GCSE English grading controversy, it is understood.
The news follows TES disclosure of correspondence showing that regulator Ofqual forced exam board, Edexcel, to dramatically shift grade boundaries that its examiners had insisted were "fair", just a fortnight before results were published.
The Commons education select committee questioned heads' leaders and Ofqual in an exploratory session this morning. But the MPs do not believe they have got to the bottom of what went on.
"There are many important questions in this to which we do not have satisfactory answers," Graham Stuart, the Conservative committee chairman told TES.
No official decision can be taken until tomorrow morning when the MPs meet again to hear from Michael Gove, education secretary, who will also be questioned on GCSEs.
But MPs from all three parties want to extend the committee's inquiries. They will call on exam boards, so they can be questioned about their role in the grading decisions.
Members are also concerned that no adequate explanation could be provided by Ofqual today for the huge disparity in results that different schools received.
Glenys Stacey, Ofqual chief regulator, told the committee this morning that the watchdog would have used its statutory power to formally "direct" Edexcel shift its grade boundaries if it had tried to stick its original position - that the board described in a letter as "fair" and backed by "compelling evidence".
Ms Stacey said the option favoured by the board would have meant "a six or seven per cent increase, grade inflation, that we did not think to be right or justifiable".
"We therefore wrote to Edexcel pointing out that they needed to bring the qualification in appropriately," she said.
Edexcel sought to play down its row with Ofqual through a further statement this afternoon, saying that the letters reflected "a moment in time".
The board said that the final GCSE English grade boundary it "agreed" with Ofqual, "took account of our concerns" and "enabled us to fairly reward learners as well as uphold the standard of the GCSE".
Its letter of August 8 paints a very different picture, making it clear that the board regarded the departure from its original "fair award" was unjustified.
Heads who this morning told MPs how unexpectedly low results had damaged pupils' futures and left teachers in tears will welcome the news of a full inquiry.
But there were less encouraging signs with reports from "a source close to Michael Gove" that the government would not order a re-grading.
"A small number getting lucky in January isn't a reason to give everyone else an inflated mark now," the source told the Spectator. "Practically nobody screaming now about unfairness agreed with us when we said modular GCSEs would be a disaster."
The source added: "Ofqual are right to fight grade inflation."