The prime minister has re-written a speech about Brexit following criticism it was factually inaccurate.
Theresa May had planned to say that both sides had accepted the result of the Welsh assembly referendum in 1997.
But she had voted against the creation of the institution following the devolution referendum.
Labour and Plaid Cymru politicians accused her of hypocrisy – and the line was dropped from the speech.
Instead, she said the result was accepted by parliament.
Members of the press had been told Mrs May, in Stoke-on-Trent, would say: “When the people of Wales voted by a margin of 0.3%, on a turnout of just over 50%, to endorse the creation of the Welsh Assembly, that result was accepted by both sides and the popular legitimacy of that institution has never seriously been questioned.”
But when she gave the speech, she said that the result “was accepted by parliament”.
Mrs May had, in 1997 after the referendum, voted against the legislation that enacted the assembly, together with other Conservatives.
Tory MP Nigel Evans said during that debate that it would have been better if the percentage majority in favour “had been in double figures”.
“That would have settled the issue once and for all, but it did not and it remains unsettled.”
The Conservative manifesto of 2005 also called for a further referendum on the assembly on expanding its powers, keeping it as it was or abolishing it.
Before the event Professor Roger Scully of Cardiff University said the result was actually won on a margin of 0.6%, rather than 0.3% – although the figure remained in the revised speech.
Labour MP for Cardiff Central Jo Stevens said the development had exposed “yet more utter hypocrisy from the PM”.
Cardiff South & Penarth MP Stephen Doughty, a leading supporter of the Best for Britain campaign for a second referendum, said: “This is a very strange example for the PM to use – not least given she herself voted against implementing the Welsh referendum result, and the Tories continued to oppose it for years afterwards.”
Labour AM Alun Davies said the briefed remarks showed “ignorance and incompetence in equal measure”.
“It is a perfect metaphor for Brexit,” he added.
‘Disregard for Wales’
Prior to the speech Liz Saville-Roberts, Plaid Cymru MP, added: “Unlike the unicorns of the Brexit referendum, the 1997 devolution vote was a clear question, with a clear outcome and clear consequences. The only party to attack its legitimacy was her party – this is hypocrisy of the highest order.
“Mrs May’s revisionist history shows a disregard for Wales, devolution and democracy.”
Former Wales Office special advisor Laura McEvatt said on Twitter that “stopping howlers like this is a pretty big reason (why) the Wales Office is still around”.
“No. 10 should have made use of them,” she said.