Scottish Secretary Alister Jack has ruled out a second referendum on independence even if the SNP win a majority at next year's Holyrood election.
The UK Tory minister also rejected Nicola Sturgeon demand for Holyrood to be handed the power over calling future referendums with a warning that it would see Scotland "plunged into neverendums."
The Prime Minister is to reply "very soon" to Ms Sturgeon's request for second vote on Scotland leaving the UK in light of the election result, but this will certainly be rejected.
Mr Jack said the prospect of Holyrood being handed control over the staging of referendums was "unacceptable."
"I've written to the Prime Minister this week and he'll be replying very soon to Nicola Sturgeon's letter of the 19th December," he told the BBC Politics Scotland.
"It's absolutely the case that constitutional matters are reserved and must remain with the UK Parliament, in the same way as defence must remain, in the same way foreign policy must remain.
"It would be wrong for us to give the right to the Scottish Parliament to set referendums and the context and the timing for the simple reason that we would then be plunged into neverendums.
"That's not good for us, that's not good for the economy."
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 past system. 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."
And despite Mr Jack having previously indicated that an SNP majority in next year's Holyrood election could be the trigger for a second referendum, the Scottish Secretary today ruled this out.
"It's about once in a generation and once in a lifetime, that's what people voted for," he said.
"We've had ten 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.
"We do not think 2021 is the time to start having more referendums, they're very divisive for our society and the time now is for us all to pull together and as one United Kingdom go forward and take on the benefits that exist."
The SNP's shadow Scottish Secretary Mhairi Black hit back at Mr Jack, insisting that the Tories have no mandate to block a second referendum in Scotland.
“The SNP won a landslide victory in last month’s general election – winning 80% on a mandate for an independence referendum, while the Tories lost more than half their MPs," she said.
“They stood on a platform of stopping Scotland’s right to choose and were humiliated at the polls – the Tories have no mandate whatsoever to block Scottish democracy.
“Whatever your views on independence, we can all agree that Scotland’s future must be Scotland’s choice – not Boris Johnson’s or his cronies.”
“Scotland voted overwhelmingly to remain in the EU and has rejected Brexit at every opportunity. And despite all the bluster from Westminster politicians like Alister Jack, we all know that a fresh referendum on Scotland’s future is in demand.
“I am confident that when the people of Scotland are given a choice on their future, they will choose to escape the mess of Brexit and the broken Westminster system to build a fairer Scotland.”