THE autumn of 2018 would be “the common sense time” for a second referendum if Theresa May rejects a bespoke Brexit deal for Scotland, Nicola Sturgeon has said.

Echoing comments by her predecessor Alex Salmond, and going further than she has before on the potential timing of another vote, the First Minister suggested Scots could return to the polls just four years after rejecting independence in 2014.

She and Mr Salmond both previously said it would be a "once in a generation" choice.

READ MORE: Budget 2017: Chancellor Philip Hammond's tax rise for self-employed is branded 'attack on aspiration' from Tories

Interviewed late last month for a new BBC documentary on Brexit, Ms Sturgeon vigorously denied she was bluffing about holding a referendum if the Prime Minister rejected her proposal to keep Scotland in the EU single market after the rest of the UK left.

The First Minister said: “There are politicians in Westminster who think Brexit and all of this is some kind of game. It’s not a game, it’s really, really serious and the implications for the UK are serious and the implications for Scotland are serious.”

Asked if she agreed with some of her SNP colleagues that autumn 2018 was a likely date for another plebiscite, Ms Sturgeon replied: “Within that window... when the 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. I’m not ruling anything out.”

As Ms Sturgeon would have to call a referendum several months in advance of holding it, the Brexit negotiations could be unclear, and future trade deals would be unknown.

Former SNP deputy leader Jim Sillars also warned this week: “I cannot conceive of the Yes movement winning in 2018 in the middle of [Brexit] negotiations. We would be subject to the cry from Westminster, ‘Why don’t you wait to see what the deal is?’”

In recent days, Ms Sturgeon’s inner circle has sought to play down speculation that she will make a major announcement on a referendum at next week’s SNP conference in Aberdeen.

Sources suggested Ms Sturgeon would hang back until after Mrs May triggered Article 50 later this month.

However the identification of autumn 2018 - Mr Salmond’s stated preference for a referendum - will inevitably increase the expectations of SNP activists.

Scottish Tory leader Ruth Davidson said: “Nicola Sturgeon has just admitted what everybody already knew - that the SNP is hell bent on taking Scotland back to another divisive independence referendum and will use any excuse to do so.

READ MORE: Budget 2017: Chancellor Philip Hammond's tax rise for self-employed is branded 'attack on aspiration' from Tories

"She needs to put the country first for once. People in Scotland don't want a second referendum, and the SNP doesn't have a mandate for one. Rather than cast our future under further doubt, Nicola Sturgeon needs to act like a First Minister, provide some certainty for Scotland, and rule it out."

Scottish Labour leader Kezia Dugdale said: “This is yet another attempt by Nicola Sturgeon to sow division and uncertainty at a time when the country needs to pull together more than ever.

“The First Minister has been all over the place – one week she threatens a vote, the next week she backs away. All this does is cause even more uncertainty for Scotland’s economy at a time when businesses are already struggling as a result of the Tories’ plans for a hard Brexit.

"Nicola Sturgeon could provide much needed clarity on Scotland's future by ruling out another independence referendum altogether.”

Scottish LibDem leader Willie Rennie added: “Nicole Sturgeon needs to understand that independence is not the economic or the emotional answer to Brexit. An independence referendum in Autumn 2018 would cause huge damage to Scotland.”