Boris Johnson is considering hiring a new adviser in Downing Street to put the Union at the heart of policy making as he formally rejects Nicola Sturgeon's demand for the right to call a second Scottish referendum.

The Prime Minister has drafted a three page letter which will reject the Scottish First Minister's demand for a second vote on independence.

Mr Johnson will issue a robust response, as early as this week, in which he will make clear that he will not allow the vote because it would undermine the centuries-old Union between England and Scotland.

The letter makes clear that the Scottish Parliament should not given the right to choose the date and the context of a repeat of the 2014 Scottish independence referendum.

Ms Sturgeon's demanded a second referendum in a report - titled Scotland's Right to Choose - sent to Number 10 days after last month's general election.

Ms Sturgeon wants another vote to take place next year, which the report argued would allow the "smoothest transition" for a separate Scotland to become an EU member in its own right.

The SNP leader intends to campaign to win over civic Scotland and the other political parties ahead of next year's Scottish elections to the Holyrood Parliament.