Plans for a £6.6bn Oxford-Cambridge rail line were previously classified as an England-only project, meaning Wales could have received extra money, a politician has claimed.
This week, however, the Treasury announced it should have been classified as an England and Wales project, but documents show it was originally classified as England-only.
The Treasury said it was a "publishing error" in a 2020 document and the project was always considered an England and Wales development.
Plaid Cymru MP, Ben Lake, said the explanation was "completely implausible".
On Tuesday, the UK government told BBC News the East-West project was being financed through its "rail network enhancements pipeline", which it said was also funding schemes in Wales.
Lake, the MP for Ceredigion Preseli, accused the UK government of reclassifying the project and "moving the goalposts".
The Welsh government did not comment directly on the Oxford-Cambridge line, but did say Wales had been underfunded in rail investment.
