In extracts of her speech released by Downing Street, the Prime Minister had been set to claim that the result of the 1997 referendum on Welsh devolution was "accepted by both sides", despite being carried by a wafer-thin 0.3% majority.
Journalists were also told she would say “the popular legitimacy of that institution has never seriously been questioned” as the key argument against attempts to force a second EU referendum.
And in 2005, Mrs May stood in the general election under a Conservative manifesto promising a second referendum to decide whether to overturn the 1997 result.
Delivering the speech in Stoke on Monday, Ms May changed the line, saying: “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 Parliament.
“Indeed we have never had a referendum in the United Kingdom that we have not honoured the result of.”
The Prime Minister also added: "The House of Commons did not say to the people of Scotland or Wales that despite voting in favour of a devolved legislature, Parliament knew better and would over-rule them. Or else force them to vote again.
But the 2005 Conservative manifesto made clear that the party did suggest that the people of Wales should vote again, stating: "In Wales we will work with the Assembly and give the Welsh people a referendum on whether to keep the Assembly in its current form, increase its powers or abolish it."
And the Prime Minister also voted for a ‘wrecking’ amendment to the 1998 Scotland Act that would have struck down legislation creating the Scottish Parliament because it “fails to create a constitutional settlement which is stable and enduring within the United Kingdom”.
“This speech is brazen hypocrisy – with Theresa May herself previously voting against a referendum result, and then standing on a manifesto that sought a second referendum to overturn it.”
And Cardiff South & Penarth MP Stephen Doughty said: "Unlike Brexit - the Welsh Assembly grew in public support after the referendum. Brexit has headed decisively in the opposite direction - which is why the people should have the final say."