Holyrood constitutional affairs spokesman Mike Russell described the argument against an IndyRef2 put forward by Scottish Secretary Alister Jack yesterday as "bogus".
Mr Jack used a Sunday television interview to rule out a further plebiscite on the constitution - even if the SNP was returned to power at next year's Scottish parliamentary elections with a majority.
The Tory minister said Boris Johnson would reply to a letter from Nicola Sturgeon requesting a Section 30 order "very soon", but suggested such a request would be rejected out of hand.
The First Minister has insisted her party's mandate to call a second referendum was strengthened by last month's general election result.
Referring to the result of the 2014 independence vote, which the UK Government insists must be respected, Mr Jack said: "It's about once in a generation and once in a lifetime, that's what people voted for."
Ian Blackford, the SNP leader at Westminster, suggested the Prime Minister knew, in his heart of hearts, that blanket opposition to an IndyRef2 would ultimately prove to be unsustainable. "This dam will be burst," he told The Herald.
He continued: "We will make sure we are building the case both for Scotland to be independent and for the right to have that independence referendum at home and abroad. So we are simply not going to let this go."
Speaking to the BBC yesterday, Mr Jack said his letter to the Prime Minister advises against allowing a second referendum on independence.
The SNP won a landslide victory in the election north of the border last month, but the minister said support for pro-union parties versus pro-independence parties had not actually changed from the 2014 referendum when 55% of Scots voted to stay in the UK and 45% to leave.
"A referendum is about a straight result, it's not about first past the post system," he said. "I still equate it to the number of people voting for Unionist parties and I don't think that that number has changed over the last five years."
He added: "We've had 10 years where Scotland has been in discussion or having referendums. It hasn't done our economy any good, we're slower than the English economy, it's not good for jobs."