A second independence referendum should not be held while Nicola Sturgeon is First Minister or even during her lifetime, the Scottish Secretary has said as Boris Johnson prepares this week to formally reject her request for the legal powers.

Alister Jack said his message to Ms Sturgeon was that the staging of any future separation vote would be a matter for her successor in Bute House and possibly her successor's successor.

As pledged by Mr Johnson during the recent Westminster election campaign, Mr Jack said the Prime Minister would not give her the powers for another referendum even if the SNP wins an outright majority in next year's Holyrood election.

He said he had advised Mr Johnson to reject Ms Sturgeon's demand that the power to call constitutional referendums be permanently transferred to Holyrood, saying Scotland would be "plunged into neverendums," with the SNP staging a series of separation votes until they won.

Mr Jack's intervention is the clearest indication yet the UK Government intends to play hardball with Ms Sturgeon by holding her to her pledge before the 2014 vote that it was a once-in-a-generation or once-in-a-lifetime event.

The Telegraph understands that the Prime Minister has drafted a "brief" letter rejecting Ms Sturgeon's demand just before Christmas, which will be sent in the next few days.