The UK Government has a hostility to devolution and there is now no trust between the administrations at Holyrood and Westminster, MPs have been told.
Scotland’s Constitution Secretary Mike Russell said the quality of dialogue has been poor and has “got significantly worse since Boris Johnson became Prime Minister”.
His comments came as he again raised concerns about the UK Government’s Internal Market Bill, which passed its first hurdle in the House of Commons on Monday.
Mr Russell told the Committee on the Future Relationship with the European Union: “There is in my view a hostility to devolution in the current Government.”
He added: “We have been in such a difficult set of circumstances for so long that it would be difficult to find a way in which we could work constructively together, there is no trust in the relationship, absolutely none now.”
The SNP MSP said the Internal Market Bill as it stands could allow a US company to take legal action to “force its way” into Scotland’s NHS and would also permit the UK Government to spend money directly in devolved areas.
While senior Tories raised deep misgivings after ministers last week admitted the Bill breached international law, on Monday evening MPs voted to give it a second reading.
The Scottish and Welsh Governments fear the impact the Bill will have on devolution across the UK, with both branding it a “power grab”.
That is in contrast to comments from Cabinet Office Minister Michael Gove, who has repeatedly described it as a “power surge” which will hand more powers to the devolved governments.
But Mr Russell, addressing MPs from his home in rural Argyll, said: “I’m very familiar with power surges.
“We have problems with the electricity supply here in Argyll all the time.
“Power surges tend to knock things out and wreck things rather than actually contribute positively.”
Jeremy Miles, the minister for European transition in the Welsh Government, said the Bill “enhances” the number of areas where powers were reserved to London and provides for ministers there to have spending powers in devolved areas.
He told the committee: “I have heard the argument repeatedly made that the Bill enhances the devolution settlement.
“I don’t accept that for a second and I haven’t had anybody point me to a section where those powers are conferred.”
Mr Russell said: “Essentially what the Bill has done is to undercut the existing (devolution) settlement.”
He added the Bill is “sneaky in another way”, saying it would allow for the actions of the devolved governments to be “overridden by the whim of the UK Secretary of State”.
Scotland’s Constitution Secretary said: “What is here is undoubtedly, without a shadow of doubt, an enormous assault on the devolved powers.”
He told MPs he believes under the legislation “all public services could be opened up to a variety of tenders and influence which the current Scottish Government would not wish”.
Mr Russell explained: “For example, an American health company that wished to operate in Scotland in a certain way and was not able to do so under current regulations could successfully go to law under this Bill and force its way in, and that is a real concern.”
He said the Bill would allow the UK Government to directly spend money in devolved policy areas – warning the cash could be spent “in opposition to the Scottish Government”.
Mr Russell suggested voluntary frameworks could have been used instead of the legislation – which sets out processes for smooth trading to continue between the four nations of the UK when the Brexit transition period finishes at the end of December.
Mr Miles noted that when Theresa May was prime minister “engagement with us a government was significantly better than it is now in relation to Brexit matters generally”.
He told the committee: “We think that much closer working is necessary at this point, given how much closer we are to the end of the transition period.”
A UK Government spokesman said: “It is categorically untrue to say the UK Internal Market Bill could open public services to privatisation.
“The Bill will safeguard the UK internal market, which is vital to Scotland’s prosperity, and open new opportunities for investment that will boost the economy.
“Holyrood, Stormont and Cardiff Bay – already among the most powerful devolved administrations in the world – will have more control over areas such as air quality, agricultural measures and elements of employment law.
“With the vast majority of powers returning from Brussels going straight to them, they will end up with many more powers than if they were members of the EU.”