London - The British government "does not believe there should be a second referendum" on Scottish independence, Prime Minister Theresa May's spokesperson said on Wednesday, following reports that she is making contingency plans for another vote.Speculation is mounting that Scotland First Minister Nicola Sturgeon will declare her intention to hold a rerun of the September 2014 vote, as a poll published Wednesday revealed rising support for independence ahead of Britain's departure from the European Union."We don't believe that there should be a second referendum. There has been a referendum, it was clear, decisive, it was legal, and both sides agreed to abide by the results of that referendum," May's spokesperson told journalists on Wednesday.Downing Street was responding to a report that it had told Scottish newspaper The Courier it was holding "contingency" talks to deal with a referendum announcement.Scotland rejected independence by 55% in 2014, but 20 months later it voted to remain in the European Union by 62%, sparking calls for a fresh vote.The battle over Scotland's constitutional future is now almost an even split, according to a new poll released Wednesday.Support has risen to 49%, excluding undecided voters, with 51% in favour of staying in the British union, a BMG poll for the Herald newspaper said.The poll was conducted after May confirmed her intention to take Britain out of the European single market.'Game on' Sturgeon, leader of the Scottish National Party (SNP), has said a second independence referendum is now "highly likely", and allies have suggested it could be as early as 2018.Former SNP leader Alex Salmond tweeted a picture of the Herald's front page story on the poll, saying: "Game on..."The SNP said the latest poll showed the independence debate is now "a virtual dead heat"."If the Tories continue with their blind pursuit of a hard Brexit, ignoring the clear view of an overwhelming majority of people in Scotland, then more and more people will see independence as the option delivering certainty and stability," said SNP chair Derek Mackay.Conducted among 1 067 voters aged over 16, the poll asked: "Should Scotland be an independent country?" with 43% saying "Yes" and 45% saying "No". The remainder were undecided or would not say.It represents a three-point swing towards independence from a similar BMG/Herald poll conducted in December.However, the survey also found 56% of Scots do not want another independence referendum before the conclusion of Brexit negotiations, expected in 2019.The Scottish parliament, in a symbolic motion, voted overwhelmingly on Tuesday to reject Britain's march towards the EU exit, with the semi-autonomous government warning Scotland would not be "humiliated".The Scottish government said the vote - backed by nearly three quarters of Scottish lawmakers from across the political spectrum - is one of the most important in the parliament's 18-year history.May warned on Wednesday that an independent Scotland "would not be in the European Union."