Education Secretary Michael Gove has hit back in the row over GCSE English grades, labelling a Welsh minister's intervention "irresponsible".
A Welsh exam board has called on regulators to agree on a "common view" on how to resolve the crisis.
The WJEC exam board - previously the Welsh Joint Education Committee - made the plea after Welsh education minister Leighton Andrews ordered it to re-award its English language GCSE following a Welsh government review.
But with the regulator in England, Ofqual, standing firm on the issue, WJEC, which sets GCSEs in both nations, is in the unusual position of having to regrade exam papers sat by pupils on one side of the border but not the other.
Mr Gove has refused to intervene despite warning that GCSEs are "unfit for purpose" and says ministers should not "meddle" in decisions made by Ofqual, which is an independent regulator.
He maintained his stance before the Commons Education Select Committee - and called on Mr Andrews to "think again", saying he had made a "regrettable political intervention".
"The other thing I would say in respect of Wales is that I believe that the children who have been disadvantaged are children in Wales," Mr Gove said.
"I think the decision by the Welsh education minister Leighton Andrews is irresponsible and mistaken and I think that he has undermined confidence in Welsh children's GCSEs."
He also said the recent GCSE saga "reinforces the need to reform the qualifications".
Meanwhile, a teaching union suggested that at least 143 secondary schools are at risk of being labelled as failing and forced to turn into academies after they were affected by the row.
And appearing before the education select committee on Tuesday, Ofqual chief Glenys Stacey admitted she would have forced Edexcel, one of England's biggest exam boards, to alter its GCSE English boundaries to avoid grade inflation.
The Association of School and College Leaders (ASCL) raised concerns about the numbers of schools which have seen their overall GCSE results drop due to the English grading crisis.
This year, secondary schools in England will be judged as under-performing if less than 40% of pupils gain at least five Cs, including English and maths, and if students are making below national average levels of progress.
Those that fail to meet the target face being taken over and turned into an academy.
ASCL general secretary Brian Lightman said the grading fiasco "could cause enormous reputational damage to these schools, and even cost school leaders and teachers in these schools their jobs, which would be a gross injustice in view of the way these results have come out".