The Scottish Secretary has said victory in the 2021 Scottish elections would not give the SNP a mandate to hold a second independence referendum.
In a U-turn on comments he made in November, Alister Jack said a majority would not legitimise another vote on leaving the union.
Before the general election he implied an SNP victory could provide a mandate.
SNP spokeswoman Mhairi Black said the general election had already shown there should be a new referendum.
Mr Jack said he had advised Boris Johnson to not grant a section 30 order.
Speaking on the BBC's Politics Scotland programme, he said: "Nicola Sturgeon has asked for the Scottish parliament to have the right to have referendums in the future at times of its own choosing.
"That is unacceptable."
"I have written to the prime minister on this subject this week and he will be replying very soon to Nicola Sturgeon's letter of 19 December."
He added: "It would be wrong for us to give the right to the Scottish parliament to set referendums and the context and the timings for the simple reason that Scotland would be plunged into 'neverendums'.
"Nicola Sturgeon has said she fully expects a rebuttal from the PM and my advice to him is to say that."
The MP for Dumfries and Galloway said that the SNP should have to wait until "a generation or a lifetime has passed".
He said that what Scotland needed now was to settle down, come out of the hated common fisheries policy, to rebuild its coastal communities and to get the benefit of trade deals.
He said: "Referendums are very divisive for our society and I think the time now is for us all to pull together as one United Kingdom, and go forward and take on the benefits that exist.
"Let's see the benefits of Brexit. They (the SNP) have talked it down as being a disaster. Let's see if the world is still spinning on 1 February and how things can be good for Scotland."
Mr Jack's SNP shadow, Mhairi Black, insisted there was demand for a fresh referendum on independence.
"The SNP won a landslide victory in last month's general election," she said, "winning 80% on a mandate for an independence referendum, while the Tories lost more than half their MPs.
"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."
Ms Black added: "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."
The Scottish Secretary's comments came the day after thousands took to the streets of Glasgow for the first of eight pro-independence marches planned for 2020.
Organisers said 80,000 people had joined the march from the city's west end to Glasgow Green in severe weather conditions.
The event was organised in the wake of last month's general election, which saw the pro-independence SNP win 48 of the 59 seats in Scotland while the Conservatives won a majority across the UK as a whole.
Power over the constitution in the UK lies with the UK government.
For an agreed second referendum to take place, a transfer of power through a section 30 order would need to be approved by Westminster.
Nicola Sturgeon has warned Mr Johnson that a "flat no" to her request - which is expected to be his response - will not be the end of the matter, and has predicted that the prime minister will eventually have no choice but to agree to her request.
She has also ruled out holding an unofficial referendum similar to the one in Catalonia two years ago, arguing that it would not lead to independence.
The UK government has said it does not support a further vote on independence.