THIS is the tightest three-way marginal in the UK, with just a few hundred votes separating Labour, the Conservatives and the SNP.

Nationalist candidate Angela Crawley won a majority of 10,100 in 2015, but at the last General Election this plummeted to just 266 - with the Tories almost doubling their vote to surge into second place.

The constituency takes in a variety of towns and villages, including Lanark, Hamilton, Uddingston, Larkhall, Carluke and Carnwath, and many interpreted 2017's result as a reflection of the strong No vote in some areas.

Ms Crawley, who lives in Hamilton, said local issues around schools, transport and health come up frequently on the doorstep. However, voters are also very aware of the national picture.

She said the 2017 result was "unique" and unlikely to be replicated.

She said: "In this General Election it's a straight fight between the SNP and the Conservatives, because traditional Labour voters are moving towards the SNP and away from the Labour Party because they don't really know exactly what they stand for, and they've not been as clear about what their position is on Brexit."

The 32-year-old said many who voted No in 2014 are now reconsidering.

But Shona Haslam, the Scottish Tory candidate, said the two key things that keep coming up on the doorstep "are a desire to stop Indyref2 and to get Brexit sorted".

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Ms Haslam is currently the leader of Scottish Borders Council, but will stand down if elected. She lives in Peebles, a 20- minute drive from the edge of the constituency.

The 45-year-old said: "A lot of people are disappointed Labour seems to have sold out to the SNP in terms of the Union.

"A lot of Labour voters are feeling very disenfranchised and are looking for a party to support that will stand up for Scotland as part of the UK."

She dismisses suggestions Boris Johnson is a problem for the party north of the Border, insisting voters see him as someone who can "get the job done".

Away from constitutional battles, she said voters are most concerned about the state of town centres.

This view is shared by Andrew Hilland, the Scottish Labour candidate, who grew up and lives in Lanark.

"Look at Hamilton, for instance," he said, sitting in a cafe in the town centre. "This is a proud, historic town with a great industrial and cultural heritage and it's just been decimated through a complete lack of investment."

Mr Hilland, 32, previously worked for former prime minister Gordon Brown. He said he felt confident ahead of December 12, adding: "What I'm saying to voters is the Tory party are the biggest threat to Scotland's place in the UK."

He argued the SNP want nothing more than further Tory austerity to fuel the case for independence.

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However he admitted Labour had "not always been as clear as we should have been" when it comes to the big constitutional debates of the last few years.

Nationally, the polls show a collapse in Scottish Labour support, but Mr Hilland takes them "with a pinch of salt".

Jane Pickard will fight the seat for the Scottish Liberal Democrats.

But with her party securing just 1,214 votes last time, she faces an uphill battle.