FORMER Conservative prime minister David Cameron has called on Boris Johnson to reject a second independence referendum if the SNP wins a majority at next year’s Holyrood election.

With the party on track to gain a majority in the Scottish Parliament vote – for the second time in the parliament’s history – he claimed it would not be “appropriate” for a new ballot on independence to take place.

Cameron spoke to Times Radio after new poll analysis from Britain Elects showed that the shift in favour of Yes has now been the most prolonged in history.

Consistent surveys in recent months have put support for independence sitting between 53% and 55% - with reports the UK Government has not published its own polling on the matter because the figure is even higher than that.

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The former Tory leader oversaw the UK during the Scottish independence and Brexit referendums. He, alongside Alex Salmond, Nicola Sturgeon and Michael Moore, signed the Edinburgh Agreement which set the terms of the 2014 referendum.

He also announced the Smith Commission following the result of the vote which states nothing prevents Scotland from becoming an independent country in the future if the people of Scotland so choose.

But now, Cameron argues that Scotland asked for a “once-in-a-generation, once-in-a-lifetime” vote. These terms were not written in the Edinburgh Agreement.

He said he had already accepted the terms set by Scotland including votes for 16 and 17 year olds.

Cameron told the radio show: "I think that was the right answer, but having had that I think it's perfectly fair to the Westminster parliament and Boris Johnson as prime minister to say that we had a referendum we decided that, not let's look at ways we can make this United Kingdom work better."

Polling expert John Curtice has previously said it would be hard for the UK Government to rule out another vote if the SNP secures a majority next year.