Pleas by the SNP for the government to step back from “breaking the 20-year-old devolution settlement” were rebuffed by the prime minister, who vowed to plough ahead.
Westminster can override the opinion – triggered by Edinburgh’s claims of a London power grab – but it would spark the biggest political crisis since the Scottish Parliament was set up in 1999.
In the Commons, Ms May insisted the devolution proposals in the bill were necessary to “maintain the integrity of our own common market”.
Later, in an inflammatory move, she backed a Scottish Tory MP’s claim that Labour and the Lib Dems have become “midwives” to the SNP’s “crusade to tear apart the union”.
An angry Ian Blackford, the SNP Westminster leader, said: “The prime minister should respect the vote that took place.
“The Tories are seeking to veto the democratic will of the Scottish parliament. This is absolutely unprecedented.
“If this government forces through the legislation without the consent of the Scottish parliament, the prime minister will be doing so in the full knowledge that they are breaking the 20-year-old devolution settlement.”
But Ms May insisted: “What the bill does is set out a mechanism that respects devolution and lets us maintain the integrity of our own common market as we work out the long term solution.
“I think this is a reasonable and sensible way forward.”
The controversy has blown up because the withdrawal bill will repatriate powers which currently reside in Brussels, including in key areas such as fisheries and agriculture.
Most will be handed to the Scottish government, but Westminster wants to retain control over some so that common frameworks can protect the UK’s internal market.
Holyrood is adamant that Westminster should not be able to legislate over any devolved areas without its explicit consent – although the Welsh assembly backed down over an identical row.
MSPs have passed emergency laws designed to protect devolved areas after Brexit: the UK Withdrawal from the European Union (Legal Continuity) (Scotland) Bill.
A looming Supreme Court ruling on the bill’s legality could determine the extent of the constitutional clash to come.
Ms May told MPs that the government’s approach was now backed by “the Welsh government and now the Welsh assembly, including Labour and Liberal Democrat members”.
“I think it is right that we go ahead with measures that not only respect devolution but also ensure that we maintain the integrity of our common market,” she added.
Register for free to continue reading
Registration is a free and easy way to support our truly independent journalism
By registering, you will also enjoy limited access to Premium articles, exclusive newsletters, commenting, and virtual events with our leading journalists
Already have an account? sign in
Join our new commenting forum
Join thought-provoking conversations, follow other Independent readers and see their replies