TOM Clarke won the largest majority of any MP in the 2005 general election.

Five years later, the Labour veteran increased his share of the vote, with two out of every three ballots cast in his name. On paper at least, seats don't come much safer than Coatbridge, Chryston and Bellshill for Labour.

Yet, if the polls are to be believed, former minister Clarke faces defeat here after 33 years representing the area. An Ashcroft poll, published in January, put the SNP on 46 per cent - three points ahead of Labour in the constituency - with the Tories lagging behind on six per cent and the LibDems on a pitiful one per cent.

The bookmakers agree that Clarke will be one of several victims of the nationalist surge. Stick £10 on Clarke, and you'll get your tenner back plus £16 profit if he holds on. Back his SNP rival Phil Boswell instead and it'll earn you just £5, despite him seeking to overturn an 20,714 majority. That anyone other than Labour would be favourite here would have been unthinkable, even 12 months ago.

So why does Labour, and the popular Clarke, have such a battle on its hands? The obvious factor is the referendum, with North Lanarkshire, which takes in the constituency, one of only four council areas to vote in favour of independence last September.

It is an argument that Clarke takes issue with. The 74-year-old, who insists he remains on course for victory next month, says several of his constituents baulk at the assumption that because they voted Yes, they are now staunchly behind the SNP.

He believes that the reputation he has built up over the years (his campaign slogan is 'there's barely a family that Tom Clarke has not helped') is a crucial asset, while he says the story of the UK-wide campaign has not been the rise of Nicola Sturgeon, but the way Ed Miliband has defied expectations.

He said: "I've had numerous people tell me how impressed they were with Ed's performances recently, particularly the way he dealt with Boris Johnson [on the Andrew Marr show on Sunday].

"We're taking absolutely nothing for granted, we're working very hard and will continue to do so. I have heard nothing that changes my mind, despite what the bookies and polls say, that a Labour member of parliament will be returned in Coatbridge, Chryston and Bellshill. I'm getting a great deal of warmth and support."

Clarke is distributing his own pledge card through letterboxes throughout the constituency, saying he will lobby to set up a commission to abolish poverty in Scotland and campaign for a new Monklands Hospital, alongside a series of national policies. They have been splashed across the last two copies of the local paper in the form of paid-for advertisements.

Despite a clear lack of affection for the SNP from Clarke, there is a refreshing lack of animosity between the two main candidates here. The Boswell family are "lovely people" says Clarke. The pair even cheered together at Cliftonhill at the weekend, as Albion Rovers lifted the League Two trophy.

Boswell said he has himself voted for Clarke on numerous occasions in the past. He says it was the Iraq War that prompted him to question his support for Labour, although he didn't vote SNP until 2010. It is a sentiment echoed in the town centre, where it is not hard to find members of the public angry at Labour and the feeling that votes have been taken for granted.

"Tom's a good guy who's been left behind by his party," the SNP candidate says. "He's been let down by policies that no longer represent what people of Scotland want. His party are pandering to middle-England, in 40 swing constituencies most of which are south of Birmingham. But I certainly don't wish him any ill."

Boswell, 51, was raised in Coatbridge, worked for a brief time as a policeman before leaving the town for in search of employment. He says four of his five siblings were also forced down a similar path, a predicament many find themselves in since the decline of the once proud steel industry.

He worked as a quantity surveyor and contracts engineer in the oil industry all over the world, before settling in Aberdeen. Boswell fist became active in the SNP in Aberdeenshire, recently relocating to Coatbridge. He won the nomination after Dr Imtiaz Majid, a local councillor, had his candidacy blocked by SNP headquarters after he failed the vetting process.

"We came into this knowing how tough it was going to be," he says. "Our canvassing results are very good, but we're not getting carried away. This whole town, my family included, were all Labour. The fact that there's even a conversation that Labour might not win here is staggering, but what we have just isn't working."