UK government plans to end independent Scottish building regulations have been condemned by a leading architect.
Peter Drummond, a senior member of the Royal Incorporation of Architects in Scotland (RIAS), said the regulations had prevented a tragedy in Scotland like that at Grenfell Tower in 2017.
The proposals are contained in the UK Internal Market Bill currently being debated at Westminster.
The Scottish government has said the bill is a "power grab" from Holyrood.
The bill is designed to ensure trade can be carried on unhindered in each of the four home nations once the UK severs its ties to the EU.
But the White Paper published ahead of the bill said "complexities in key sectors such as construction could arise, were differences in regulations to emerge over time".
It said if England and Scotland were to have different building regulations or processes for obtaining construction permits, it would become "significantly more difficult for construction firms to design and plan projects effectively across the UK."
But Mr Drummond, the influential Chair of Practice at the RIAS, said Scottish building standards imposed significantly higher standards on construction projects than those in England and Wales.
What else could the bill do?
The aim of the UK Single Market Bill is to prevent any trade barriers between the four home nations.
Goods or services approved for use in any part of the UK will not be able to be restricted in other home nations.
There are to be common standards for professions carrying out their work, and any barrier to that would be illegal.
- Scottish regulations banning flammable cladding which remained in use in England would be against the law
- Architects would be unable to stipulate Scottish materials to reduce a building's carbon footprint as that could be construed as discriminating against other parts of the UK
- Loss of a Scottish compliance regime for design and construction would limit architects' ability to specify local forms of construction
Mr Drummond said that in 2003, following a fire in high-rise flats in Irvine, the Scottish government introduced measures to protect occupants of residential properties from the sort of tragedy that unfolded at Grenfell in 2017.
A disabled pensioner died in the 1999 blaze with five other people injured after the fire travelled up the external cladding of the recently refurbished block.
Mr Drummond, who frequently gives expert evidence in major planning and public inquiries, said: "Against that backdrop it is simply inexplicable that the bill seeks to align the more robust Scottish regulations with the English system.
"Those powers are now to be removed. The lowest common denominator within the UK will apply.
"And that is, on any fair reading, a spectacularly poor step backwards. We should all be concerned."
Following the Grenfell Tower tragedy, in which 72 people died, changes governing building safety were made on both sides of the border.
Construction law expert Cassandra Auld, of Glasgow solicitors Weightmans, writing in 2019 before new Scottish regulations came into force, said they were more advanced than those in England.
She wrote: "Developers with a significant presence in this market will have to navigate more regulatory hurdles once Holyrood turns its proposed regulations into law this year."
Writing in the trade magazine Building, she added: "It's unclear if the regulatory environment in England will eventually echo the wider safety measures proposed by Holyrood, or expand the combustible materials ban to match the criteria of buildings in Scotland."
Architects fear such different approaches could be lost if the bill, which receives its second reading this week, goes through unchecked.
Constitution Secretary Michael Russell said ministers were determined Scotland should maintain existing high standards in trade and the professions, but claimed the bill would render that meaningless as regulations could be changed at any time by Westminster.
He said: "The 'UK Internal Market' White Paper cited building regulations as an example of a potential barrier to the functioning of the UK internal market.
"There is no credible evidence to support this view.
"Differences in building regulations between England and Scotland have existed for decades and do not present significant issues for those providing goods or services or to those delivering our built environment.
"The construction sector is familiar with such differences and these are well managed."
The Scottish government has also said that under the bill any regulatory measures that could "directly reduce price competition" were ruled out.
Ministers said this meant Holyrood could, for example, have not have enacted its policy of minimum unit pricing of alcohol, which the government has said was "vital to public health."