Next month, we go to the polls to elect a new Prime Minister, and while the UK result is far from clear, the pundits are saying in Scotland it’s a foregone conclusion.

But how is the battle for the heart of Scotland playing out?

Independent polling expert Mark Diffley says: "Marginal seats present opportunities and risks for all the parties. Each of the big three is defending marginal seats, and all four main parties have at least one second-place challenge.

"We really do need more new Scotland-specific polling information that takes in recent events. This lack of research is important. UK-wide polling suggests the Tories experienced an uplift in support when Boris Johnson became PM, and again when he renegotiated the deal with the EU, but we don’t know whether this is being reflected in Scotland.

"Broadly, if you put the latest polling numbers into a seat predictor, you come up with 50 seats for the SNP. But there are many reasons to be cautious.

"First, the aforementioned lack of up-to-date polling. Second, with so many marginals it doesn’t take much deviation from a national swing to cause some interesting results in individual seats.

"Third, there are likely to be different campaigns and narratives running in different parts of the country. What a national predictor assumes is that all seats behave in the same way, for example that all the Tory gains in the north-east of Scotland will go back to the SNP."

The Herald on Sunday looks at three key marginals and asks the incumbent and the main challenges how they are framing their campaigns.

Stirling

2017: Conservative win.

Majority: 148

HeraldScotland:

Incumbent: Stephen Kerr

"I’m framing my campaign around two things: Nicola Sturgeon’s plans for the second independence referendum next year and getting Brexit sorted.

The Prime Minister will carry the load on Brexit. What I’ll be making clear is my opposition to referendums – they are divisive and I will never vote for another one. We should focus on health, education, law and order, housing. These are the things people in Stirling really care about.

People who voted Remain in 2016 and No in 2014, if they are democrats, will accept the result of 2016 referendum. People are telling me they just want to get Brexit done so we can move on. The majority of people in this constituency are unionists and democrats, and I’ve done everything in my power to argue for a pragmatic and sensible Brexit.

The people of Stirling know I am a moderate, centrist, one-nation Conservative, as is Boris Johnson at heart. They object to Nicola Sturgeon commandeering their votes to suggest they want the break-up of the UK. I’m finding people are stronger in their commitment to the union than ever and come December 12 they’ll be voting for that."

Challenger: Alyn Smith, SNP

"The last few years have left me with a seething frustration that our problems are not coming from Brussels or Strasbourg, they’re coming from Westminster. I’m definitely hearing that reflected view on the doorsteps of Stirling.

The Scottish Tories could have had huge influence at Westminster by acting as a bloc. Had they tried to find compromise, they could have been much more effective. Instead of that they appointed themselves as human shields for whatever Boris Johnson and Theresa May said.

I’m finding that No-voting Remainers are much less keen on No than they used to be. The Tory party under Ruth Davidson doubled down on unionism rather than conservatism. I’m noticing that moderate centre-right voters are coming over to the SNP. People who used to vote Labour are coming to the SNP, too.

Since 2017 the people of Stirling have had a Brexiteer MP who has argued for a deal, and for no-deal, depending on which way the wind was blowing, and now uses Ruth Davidson on his leaflets, even though she is no longer leader of the party.

I’ve spent the last three years in Europe fighting for Scotland’s voice to be heard. We can stop Brexit. But Scotland should also have the right to choose a different future for itself."

North East Fife

2017: SNP win

Majority: 2

HeraldScotland:

Incumbent: Stephen Gethins

"It’s becoming increasingly clear that people who backed Remain are coming over to the SNP as the biggest and strongest pro-European voice at Westminster. I’ve been especially pleased at the large number of LibDems who have decided to vote for me for the first time, including Fife’s former Provost, Frances Melville.

I’ve also been encouraged by people from other parties coming on board, such as my previous opponent from the Scottish Greens.

It’s so important that in this election we don’t let the Tories come through the middle and return an unrepresentative Conservative who will merely do Boris Johnson’s bidding and deliver his damaging Brexit."

Challenger: Wendy Chamberlain, LibDems

"I was selected over a year ago and have been campaigning ever since. People on the doorsteps know and recognise me, and the LibDems have a long history here, through Menzies Campbell, Willie Rennie and all our councillors.

Brexit is a big issue for some, but so is the prospect of Scotland leaving the UK. There are local issues at play, too, such as GP out-of-hours services and the ongoing work on Madras College, and we have a powerful message on those issues, too.

Remainers who don’t support independence are coming to us. People don’t like feeling that they have to choose a union. I’m not meeting many Remain voters on the doorstep who want a second referendum. You don’t solve the problems of breaking up one economic union by breaking another."

Glasgow North East

2017: Labour win

Majority: 242

HeraldScotland:

Incumbent: Paul Sweeney

"Our recovery at the last election wasn’t expected and I’ve never taken it for granted. It provided a precious opportunity to restore trust in the Labour Party and I’ve given this job everything for the last two-and-a-half years.

I’ve immersed myself in local grassroots issues like the closure of the Caledonian railway works in Springburn and the campaign to save Whitehill Pool in Dennistoun.

Brexit rarely comes up on the doorsteps. The decline in council services, facilities under threat, housing, benefits and poverty are the issues people want to talk about.

But the voters here seem quite happy with Labour’s approach to have a second referendum on EU membership. They think it makes sense.

Indyref2 is not an issue for this election. What’s at stake is whether we get a Tory or Labour government.

Jeremy Corbyn says if there is a clear mandate at the Holyrood election in 2021, then no UK government can stand in the way. But I don’t see that mandate becoming a reality."

Challenger: Anne McLaughlin, SNP

"Other than the key message about putting Scotland’s future in Scotland’s hands, I’m focusing on the fact that I’m a practical community activist. I carried on serving, campaigning and volunteering when I lost this seat back in 2017. But I can do so much for the people of this constituency if they re-elect me.

People want an MP who listens, will fight for them and understands them. In 2017 people assumed I was a shoo-in and stayed at home – that lost me the election. No one can take anything for granted. Things can change very quickly and none of the candidates knows what will happen.

Brexit is a big thing on the doorsteps – it is turning people towards independence. They feel betrayed by the categorical assurance given during the 2014 referendum campaign that voting No was the only way to keep Scotland in Europe.

Most people in this constituency voted Yes in 2014. I haven’t met anyone who’s moved from Yes to No, but plenty moving from No to Yes.

How unrepresentative the likes of Boris Johnson and Jacob Rees-Mogg are is also a factor. That’s why it’s so important for people in Scotland to take the decisions about their own future."