Helle Thorning-Schmidt makes a last-minute warning to voters over Denmark's prized welfare system, as a campaign characterised by aggressive skirmishing over immigrants draws to a close.

Danish Prime Minister Helle Thorning-Schmidt has warned that the Right-wing opposition will cut the country’s prized cradle-to-grave welfare system, in a last-minute bid to win over undecided voters ahead of an election that is still too close to call.

The latest poll of polls by Berlingske newspaper gave the Right-wing opposition parties a slender 1.4 percentage point, or single seat, lead over the Social Democrat-led government and its allies, ahead of Thursday's poll.

“Throughout the election campaign, the Right-wing parties have refused to answer how and [by] how much they will cut social assistance, and there is also talk of cutting unemployment benefit and disability pensions,” Ms Thorning-Schmidt warned in her final press conference of the campaign on Wednesday morning.

Kasper Hansen, a politics professor at the University of Copenhagen, said that the election would be won by the party that manages to control the agenda on the final day.

“If they are able to switch the agenda on to the welfare issue, they are going win the election,” he said. “It’s so close, it's not possible to call in any way, so even a few thousand voters will be decisive.

"The Social Democrats will keep talking about welfare, while the Right-wing parties will talk about immigration.”

Ms Thorning-Schmidt, who is married to Stephen Kinnock MP, the son of the former Labour leader Lord Kinnock, has over the past two years executed an impressive political turn-around. She has demolished a 27.8 percentage point lead held by the Right-wing parties by taking credit for Denmark’s economic recovery, ruthlessly exploiting an expenses scandal besetting her rival Lars Loekke Rasmussen, and moving sharply to the right on immigration.

She set the tone for the election campaign in her New Year’s speech, when she declared: “If you come to Denmark, you must of course work. You must learn the Danish language, and you must meet and mix with Danish colleagues.”

The government then brought in tighter immigration rules, making it harder to claim asylum and easier to send refugees back if the situation in their home countries improves.

Then when the campaign began, the slogan “If you come to Denmark, you must work” was plastered over buses around the country, since when Ms Thorning-Schmidt’s own rhetoric has become ever tougher.

In the campaign, both sides have pledged to reduce “welfare tourism,” deny unemployed migrants permanent residence, and limit family reunion. The shift has agonised the Social Democrats’ allies.

“I think that the debate about refugees and asylum seekers during this election has been downright shameful,” argued Uffe Elbæk from The Alternative, a new green party, in a debate on Tuesday night.

The opposition have responded by moving even further to the right, with the Conservative Party rolling out “Stop Nazi Islamism” posters, and the Liberal Party demanding “an immediate halt” to a “nearly explosive influx” of asylum seekers.

The populist Danish People’s Party, which more than any other party has been responsible for shifting the immigration debate to the right in Denmark, has been able to sit back and largely leave the anti-immigrant rhetoric to its partners, instead focusing on increased social spending and the on EU, where it has positioned itself as Britain's main partner in the quest for reform.

On Wednesday, the party released an advertisement quoting Ms Thorning-Schmidt saying "I am a European by heart". "Tomorrow we are voting on the EU," the party's lead MEP Morten Messerschmidt said, as he tweeted out the advert.

Ian Manners, a professor at the University of Copenhagen, told the Telegraph that the party would exact an "enormous price" from the largely pro-EU Liberal Party to join a government coalition.

“They would want a referendum on Europe, which I don’t think the Liberals could accept," he said. “I suspect that if they were to be tied in, they would make treaty revision part of their agreement."

It seems to be working: the latest poll of polls gives the Danish People's Party 17.8 per cent of the vote, up from 12.3 per cent in 2011.

Voting will close on Thursday at 8pm Danish time, with the first exit poll released at the same time. The preliminary count is likely to be completed around midnight.