Britain's party leaders are making a last-ditch appeal for votes on the final day of campaigning ahead of the General Election.

The leaders are continuing their whistle-stop tours of key seats across the country today, combining positive messages with warnings about the consequences of their opponents taking power.

The main parties are locked in a tight race ahead of Thursday's vote, with polls suggesting the final flurry of campaigning has not led to a decisive breakthrough for either the Conservatives or Labour.

An ICM poll for The Guardian released on Wednesday evening has the two parties level on 35%.

Earlier in the day, David Cameron met shift workers during a through-the-night campaign bus trip before visiting a farm in Brecon.

He later stopped to see construction work at Chester Zoo, before moving on to a housing development in Lancaster.

In an interview with Sky News, the Prime Minister spoke about the possibility of a renewed Liberal Democrat coalition if the Tories fail to claim a majority.

He said he wants to carry on pushing for a majority Tory government, but added he will "always do the right thing by the country" when asked if he is ready to consider a second coalition.

Mr Cameron appeared to concede that there is only one party he would not have any conversations with in the case of a hung parliament.

"The SNP is different because they don't want a Westminster government to succeed," he said.

"They don't want the United Kingdom to succeed. They don't want the United Kingdom to exist."

He said it was "out of the question" that the Conservatives would have any discussions with Nicola Sturgeon's party.

Asked about if he could work with the Lib Dems after a bitter campaign, he replied: "What I've said is I will always put the interests of the country first.

"That is what a Prime Minister should do, that is what I do.

"Now I believe the best interests of the country are an overall Conservative majority... but I'll always do the right thing by the country."

Campaigning across Lancashire and Yorkshire, Labour leader Ed Miliband has insisted he is "not countenancing defeat" and warned another coalition between the Conservatives and Liberal Democrats posed a "huge risk" to working families.

He said: "My focus is on winning a majority, my focus is on the British people and the huge choice they make."

The only way to get David Cameron out of Downing Street was by voting Labour, Mr Miliband insisted.

Meanwhile, Labour's deputy leader Harriet Harman said she would "not engage in post-match speculation" ahead of Thursday's vote.

Insisting Labour was not involved in discussions with other parties about possible post-election pacts, Ms Harman told Sky News: "We are not having discussions behind closed doors with anybody from other parties, because our agreement and our discussion is with the British people.

"That's who we are asking to vote for us.

"Our commitment and our contract is with them, not some shady deals that we do now behind closed doors."

Lib Dem leader Nick Clegg, who was to complete the second half of a 1,000-mile campaign tour from Land's End to John O'Groats, said voters faced "the biggest political decision of their lives".

He told Sky News: "I really believe in what the Liberal Democrats are trying to do, which is to keep our country stable, to make sure the next government is decent, that we govern for the whole of the United Kingdom, that we don't see it pulled apart.

"I really, really worry that there is going to be this lurch to the right with the Conservatives, lurching off and imposing ideological cuts on our public services, dancing to the tune of UKIP.

"Or a lurch to the left as Ed Miliband and Ed Balls borrow pots of money, dancing to the tune of Alex Salmond.

"We are now the guarantors of stability and I think that's what people want from our country."

He added: "I think we were written off at the beginning of this campaign.

"I believe we will be the surprise story in this election."

Meanwhile, UKIP leader Nigel Farage made an eleventh-hour push for votes in Thanet South where he gave as good as he got in a verbal exchange with a heckler.

On the campaign trail in Kent, Mr Farage also criticised the negativity of the General Election campaign and felt it made the case for a change in the voting system.

He said: "We have spent the last two to three weeks talking about who would get into bed with who.

"We have spent the last last two to three weeks with the big parties saying well you shouldn't vote for the other party.

"We have got totally negative politics in this country.

"I am beginning to think that that's a product of the first-past-the-post system 'Please vote for me, we are not quite as ghastly as the other people'.

"If we had a form of PR you might actually get people saying 'vote for us because this is what we stand for'."

Campaigning in Colchester, Chancellor George Osborne argued the country would want "to keep a strong economy and David Cameron in Downing Street" rather than "a weak Ed Miliband propped by by the Scottish nationalists".

Speaking in Scotland, Ms Sturgeon said: "All politicians have got a duty on Friday morning to respect the outcome.

"And if the voters across the UK decide not to give Labour of the Tories a majority then that means they want parties to work together.

"If there's an anti-Tory majority on Friday morning we should work together to get the Tories out." 

We will have full coverage of the UK election on Newstalk.com tomorrow.