The conversation on the doorstep in Bents Green began so promisingly for Nick Clegg. The economy was going well, noted his Sheffield Hallam constituent, a 53-year-old quantity surveyor. Business at the man’s engineering firm was booming and they were taking on new staff. The deputy prime minister nodded enthusiastically. Then he heard the n-word.

“I must admit, I normally vote for you,” said the man. “But this time I’m going for Ukip, purely because of Europe and immigration. I don’t trust Farage, but I will probably vote for them.”

Things didn’t really improve from there. “I think he [Farage] will be in coalition instead of you next time,” said the man, who declined to be named. Well, Clegg wasn’t going to let that one pass. “I doubt that very much,” he began, as two bodyguards waited patiently at the gatepost, muttering to each other via their earpieces. “But here, in your neck of the woods, the choice really is between myself and the Labour party. Ukip aren’t going to win here.”

Though Clegg didn’t mention it, Farage’s party hasn’t even selected a candidate yet to try to eat into his 53.4% majority this May.

“I do like you,” said Clegg’s lost voter. “We’ve been to hear you talk and we really appreciate having a national politician taking the time to come local.” Clegg spluttered good-naturedly: “Then the least I deserve is a cross on your ballot paper!” The conversation ended with Clegg noting that both he and his interlocutor were wearing North Face fleeces. “Look at that, we’re both wearing North Face and still you won’t vote for me. What does it take?”

Nick Clegg canvassing in Sheffield Hallam. Photograph: Christopher Thomond/Guardian

Despite such dispiriting encounters, Clegg insists he is “confident but not complacent” about retaining the seat he has held since 2005. In the leafier parts of the semi-rural constituency in south-west Sheffield it is easy to find voters, particularly older people, who are keeping the Lib Dem faith, insisting Clegg is a hard-working local MP who has been unfairly scapegoated by the media.

Many will tell you they have not forgotten the “socialist republic of South Yorkshire” of the 80s, which they feel led to poorer (Labour-voting) parts of Sheffield getting preferential treatment – a divide some say continues today.

It is therefore quite remarkable that Clegg now sees Ed Miliband’s party as his main challenger. Labour has never won the seat in its 120-year history, or even come close. Yet a recent poll by the Tory peer Lord Ashcroft gave Clegg a lead of just three points over his young Labour rival, Oliver Coppard. Ever optimistic, Lib Dems hope the 23.5% of the electorate who voted Tory in Sheffield Hallam in 2010 will hold their noses and vote for Clegg in May if it will keep Miliband out.

The Labour surge cannot be attributed merely to vengeful students bitter about Clegg’s broken promise on tuition fees. Despite sharing a name with one of Sheffield’s universities, only 15% of the electorate are students. Students live mainly in the Crookes and Ecclesall wards, where Clegg’s name was greeted last week with responses ranging from “tosser” (a locksmith on Crookes Road), and “Cameron’s pet” (a taekwondo instructor from Crosspool who said he was switching from the Lib Dems to Ukip in May), to “lying bastard” (a barman, a Lib Dem to Labour defector, at the Ball pub in Crookes) and “unprincipled, power-grabbing charlatan” (the owner of Books on the Park at Hunter’s Bar).

The only South Yorkshire seat that is not a Labour stronghold, Sheffield Hallam is often described as the most affluent constituency outside the south-east. Labour came third in 2010, when Clegg upped his majority to 15,284 with the Tories a distant second. Yet just before Christmas the Times suggested on its front page that Labour was mounting a secret operation to “decapitate” Clegg. After a visit to the constituency, the Labour MP Tom Watson stirred the pot by saying: “I have never encountered such animosity on the doorstep against an incumbent MP – particularly one as high-profile.”

Despite the rhetoric, Labour is not putting any money into fighting the seat. It is not on the party’s target list, and Coppard has not been given the services of a paid organiser, nor “mobilisation assistants”. Clegg, meanwhile, has registered donations to his local party worth £43,500 this year, cash that helps to pay for two full-time campaign staff, not to mention an avalanche of leaflets that pensioners were busy stuffing in envelopes in a church hall in Bents Green on Saturday morning.

Labour’s Oliver Coppard. Photograph: Christopher Thomond/Guardian

Coppard has had to pay for his own propaganda, raising money via a “donate” function on his website. His campaign is run by Harry, who works in a bicycle co-operative by day and often turns up to canvassing sessions on his bike wearing a head-torch and no coat. He has co-opted an army of students, who will trek up Sheffield’s hills in foul weather in the hope of kicking out the man they blame for their £9,000 tuition fees.

On the doorstep, Coppard paints a picture of Clegg as an absent MP more concerned with cosying up to Cameron than fighting for his constituents. Clegg has made Coppard’s job easier, not just by reneging on his pledge not to increase tuition fees but by being in the highest echelons of a government that, shortly after its formation in 2010, cancelled a £80m loan to Sheffield Forgemasters, which the steel company had hoped to use to buy a new forging press for producing nuclear plant components, creating jobs.

Coppard, the amiable son of a former chief executive of Barnsley council, was once an office junior for another Sheffield MP, Meg Munn, and like many of the new Labour generation he loves American politics, having interned in Congress and worked on Obama’s second presidential campaign. After a spell at a London-based thinktank, he now works for the South Yorkshire local enterprise partnership trying to make the county’s former coalmining communities carbon-neutral.

A first-time general election candidate who went to school in Sheffield Hallam, he is green enough to believe he can topple Clegg, but says: “This is not a decapitation strategy. This is a local campaign, about us doing our best to win a seat we can win.”