Nicola Sturgeon's call for a second Scottish independence referendum has been dismissed as "unwanted and unworkable" as her letter reached Number 10 on 31 March.

The SNP leader sent the document to Theresa May after Holyrood backed her call for another ballot between Autumn 2018 and Spring 2019 by 69 votes to 59 on Thursday.

Sturgeon, who has been First Minister of Scotland since 2014, told the UK prime minister that her mandate for another plebiscite was "beyond question" and argued that it would be "democratically indefensible" if May failed to grant the vote.

But Jackson Carlaw MSP, the deputy leader of the Scottish Conservatives, said Sturgeon's proposal was both ""unwanted and unworkable" until voters north of the border have a chance to see Brexit play out.

"At the very moment we should be uniting as a country to get the good deal out of Brexit, Nicola Sturgeon is trying to divide us again. Her plans are unwanted and unworkable," said Carlaw.

"Unwanted, because people made a decision on this just three years ago and don't want to go back to yet more division.Unworkable, because under the SNP's plans, people would have no idea what they are voting on.

"She wants a referendum campaign to start right now – despite still not having answered basic questions on the currency, on EU membership and the cost of independence."

The comments come just days after May invoked Article 50 of the Lisbon Treaty and started divorce talks with the EU. The Brexit negotiations are expected to last two years, with a deal decided in 2018 and then ratified in 2019, according to EU Commissioner and chief negotiator Michel Barnier.

Sturgeon called for the second independence referendum after 62% of Scottish voters backed Remain at the EU referendum in June 2016. The latest opinion poll from Panelbase, of more than 1,000 people between 13 and 17 March, found that 42% of respondents wanted to breakaway from the rest of the UK.