NICOLA Sturgeon has appeared to signal she may leave office before the next Scottish Parliament election.

She dropped the hint during Monday’s BBC Question Time special, saying she would be judged in the 2021 poll “if I’m asking people to vote for me again as First Minister”.

It is very unusual for political leaders to talk about “if” they will stand for re-election, with even the most beleaguered trying to exude an air of invincibility.

The comment came after Ms Sturgeon was asked why her personal ratings had slumped, was jeered for failing to rule out a third independence referendum, and was told her party’s record on public services was “hopeless” by members of the Question Time audience in Edinburgh.

One audience member, Andrew Couch, asked her: “You’ve said that you want to be judged on education. On that basis shouldn’t you resign?”

Recent international surveys have shown declines in maths, literacy and science in Scotland.

Ms Sturgeon insisted her government was working on reforms, and giving more money to headteachers to help them close the attainment gap between rich and poor pupils.

She then said: “When we come to contest the next Scottish elections, if I’m asking people to vote for me again as First Minister, I expect to be judged on that.”

She did not expand on the remark, which was not the subject of any follow-up questions.

By the 2021 election, Ms Sturgeon would have been First Minister for six and a half years, and if she stood for re-election would be asking voters to extend her term to 11 and a half.

The SNP would also have been in power 14 years, and would be asking to stay there for 19.

Few parties or leaders manage that long in office before public opinion turns against them.

Margaret Thatcher lasted 11 and a half years before being dethroned by her own party, while Labour’s Tony Blair stood down after a decade, and Tory David Cameron said he would only serve two terms as Prime Minister, before being forced to resign over Brexit.

Ms Sturgeon may be calculating that by 2021 the SNP’s best chances of being returned for a fourth term would lie with a fresh face.

Other reasons why she might quit Bute House include continued failure to improve Scotland’s education record - something she has made the defining benchmark of her administration.

She would also be expected to resign if she held and lost a second independence referendum.

The whiff of political mortality comes a week after an Ipsos Mori survey for STV found Ms Sturgeon had fallen from Holyrood’s most popular leader to least popular in a year.

For the first time, her personal approval ratings had entered negative territory, falling from +14 to -4 since September, with 50 per cent of people dissatisfied with her performance compared to 48 per cent satisfied.

Scottish Labour leader Kezia Dugdale has ratings of -2 in the same survey, while Ruth Davidson was +5, LibDem leader Willie Rennie +6 and Green Patrick Harvie +12.

A new YouGov poll commissioned by Scottish Labour has also found very few people believe Ms Sturgeon’s claim that education is her “defining mission” in government.

Almost two-thirds of those polled, 62 per cent, said independence was the the First Minister’s top goal, with just six per cent saying the NHS, five per cent saying more jobs, four per cent protecting local services, and just three per cent saying “improving Scotland’s schools”.

Scottish Labour’s General Election campaign manager James Kelly said: “The tide has turned against Nicola Sturgeon, and her popularity ratings are in freefall.

“Voters are angry that the only thing she cares about is a divisive second referendum.

“This General Election won’t get rid of the SNP in Holyrood, but voters can do that in 2021 – and with her record tatters, Nicola Sturgeon will be absolutely terrified of facing the public.”

Tory MSP Adam Tomkins said: “I would read it as a recognition the the big question in Scottish politics is beginning to shift away from the constitution to the SNP’s record in government.”