Downing Street has said continued discussion about the prospect of a second Scottish independence referendum is "a distraction".
It comes after Scotland's First Minister Nicola Sturgeon insisted she is "not bluffing" about holding a second Scottish independence referendum.
Speaking on BBC Two's Brexit: Britain's Biggest Deal, Ms Sturgeon said she was "not ruling anything out" when asked about when the referendum might take place.
She also warned politicians in Westminster that Brexit is not "some kind of game".
When asked about autumn 2018 being a likely date, Ms Sturgeon said: "Within that window. I guess when the sort of outline of a UK deal becomes clear on the UK exiting the EU, I think would be the common sense time for Scotland to have that choice, if that is the road we choose to go down.
In response to the First Minister's comments, a Downing Street spokesman said: "Should there be a second referendum? No, we don't believe there should.
"The referendum was held only in 2014. It was a fair, decisive and legal vote.
"Both sides agreed to abide by that and we think both sides should.
"Continued discussion around a second referendum is a distraction," the spokesman added.
While the UK narrowly voted to leave the EU, almost two-thirds of Scots who took part in the ballot wanted to remain part of the bloc.
Writing in The Times newspaper last week, Ms Sturgeon said she had chosen to hold off exercising her mandate immediately to explore other options to protect Scotland's place in Europe.
Ms Sturgeon has put forward proposals for a "differentiated deal" which could see Scotland remain part of the European single market through membership of the European Economic Area.
In January, former first minister Alex Salmond said a vote on Scottish independence could take place in autumn 2018.
The ex-SNP leader made the suggestion after his successor Ms Sturgeon warned the Prime Minister's plan to take the UK out of the European single market "undoubtedly" makes another vote on the future of the UK more likely.
In the September 2014 referendum Scots voted by 55% to 45% to stay part of the United Kingdom.