Conservatives and Liberal Democrats are braced for losses as voters go to the polls in local elections following a campaign that has been dominated by Ukip.
Liberal Democrat leader Nick Clegg has not ruled out coming fourth to Ukip, while Tory fears that the party will eat into their vote have led to an increasingly bitter war of words.
Bookmakers are predicting Nigel Farage's candidates could scoop more than 100 seats, and Prime Minister David Cameron acknowledged that Conservatives face losing votes to Ukip.
Nick Clegg has not ruled out coming fourth to Ukip
And in a further blow to David Cameron, The Sun newspaper has refused to endorse the party - despite switching its allegiance to the party in 2010 general election.
The paper said in its editorial: "Today, as 18 million people have the chance to elect new local councils, none of the big four deserves our support. Tories, Labour, Lib Dems and yes, even UKIP, have all proved beyond your trust."
The paper urged readers to just chose the best local candidates.
"Of course it's mid-term, the Government has had to make difficult decisions, we're responsible for making a series of difficult cuts and difficult choices," Clegg told the BBC on Wednesday.
"I think people understand that but often it's not welcome and often it can lead to people feeling frustrated."
Nearly 10,000 candidates are battling for seats at 34 English top-tier counties and unitary authorities as well as the Isle of Anglesey council in Wales.
"You know, we have been beaten by Ukip before in the polls," the Deputy Prime Minister told Channel 4 News last night.
"What I am saying is that these things come and go in politics and I've seen them in my time come and go.
"Ukip beat us in 2009; a year later we won 24% of the vote in the general election and Ukip were nowhere."
Although mid-term elections are traditionally expected to favour opposition parties, Labour is playing down expectations of making significant gains with sources keen to stress the local authority elections are mainly being staged in Conservative heartlands.
In South Shields, votes will be cast to return an MP in a parliamentary by-election triggered by former Foreign Secretary David Miliband's decision to step down to become head of the International Rescue Committee in New York
Labour leader Ed Miliband said he was "certain we can overcome our country's problems".
He added: "The choice is between a One Nation Labour party that knows we rebuild Britain by standing up for the many and a Conservative-led government that only stands up for the few."
Ukip is fielding over 1,700 candidates in Thursday's polls, only just behind Lib Dems.
William Hill and Ladbrokes are both predicting the anti-European Union party will return in excess of 100 seats.
After polls close at 10pm early results that should indicate how the parties are doing are expected to come from Staffordshire, East Sussex, Dorset, Hampshire and Lincolnshire.
The first full council result is likely to come from Lincolnshire at around 2.30am tomorrow. The Tories have had control of the council since 1997.
Votes are also being held in mayoral elections in Doncaster, where incumbent Peter Davies, who resigned from the English Democrats, is fighting for re-election as an independent, and North Tyneside.