The Liberal Democrats are braced for a "difficult" night on Thursday, with the party set for an electoral mauling in both local and European contests.
In a late rallying cry ahead of the elections, Nick Clegg will issue a fresh warning about Ukip and Tory eurosceptics, claiming if the UK severed ties with Brussels they would "hand the keys" to running Europe to the French and Germans.
But the party acknowledged his unashamedly pro-European message is up against "quite extensive hostility in the country" towards the EU.
A senior source said: " We want to return as many Liberal Democrat MEPs and councillors as possible.
"But... we are fighting these elections in much more difficult circumstances than we did last time around, as a party of government and in the face of, frankly, some quite extensive hostility in the country towards Europe."
Even in 2009, when the European election was fought in "relatively benign circumstances" for the Lib Dems, the party finished fourth with 13% of the vote.
The Lib Dems' hopes rest on getting their vote out in the strongholds where they have Westminster MPs, the source said.
"It's going to be a difficult night for the Liberal Democrats on Thursday. We are fighting this election as a party of government... by definition we've not fought a Euro-election like that before.
"These are often tougher for us than others.
"What I hope you will see... is that when the results come in, there will be areas where we don't have a particularly strong presence, where we aren't able to get out on the doorstep, where we will do badly.
"But the key things for us to look at, particularly with the focus of 2015, is how we are doing in the areas where we are able to get out on the doorstep and get our message across, how we are doing in our held seats and target seats."
In areas like Mr Clegg's Sheffield Hallam seat, the Lib Dem vote is holding up in the face of a Labour effort to claim a high-profile scalp in 2015, and voters are drifting from Ed Miliband's party to Ukip, the source claimed.
Ahead of a potential wipeout for the Lib Dems in the European vote and a further erosion of the party's local government powerbase in the council elections, Mr Clegg's leadership has been the subject of fresh speculation.
But the senior party source said: "Barely a week or month has gone by, certainly no election or conference period has gone by, without somebody saying there is going to be a leadership challenge, or this is the straw that will break the coalition, or this is what will be the final nail in the Liberal Democrats' coffin. And they never materialise."
Mr Clegg's attempts to characterise the Lib Dems as the "party of in" will continue i n a speech to the European studies centre at St Antony's College, Oxford, where the Deputy Prime Minister will hail the EU as "the most successful example of international co-operation in modern history".
In a warning to the "false patriots" calling for a British exit, he will say: " Ukip. Conservative backbenchers. Isolationists. They are not thinking about Britain's interests. They shroud their narrow nationalism in the language of patriotism.
"They mask their hostility towards Europe as British bulldog spirit. But these are false patriots.
"The isolation they offer is a breach of our history, of our great British tradition of engagement, and of our enlightened national self-interest. If the forces of insularity and chauvinism get their way they will ensure that Britain no longer benefits from the political and economic advances in Europe that we have shaped.
"And they will hand the keys to running our European continent to the Germans, the French and others, while we retreat back across the English Channel."
But Mr Clegg will insist the Lib Dems are not "starry-eyed about Brussels" and have a clear programme for reform of the EU.
The Deputy Prime Minister gambled ahead of the election by holding two head-to-head debates with Nigel Farage, contests that opinion polls suggested had been won by the Ukip leader.
But the Lib Dems claim they led to increased scrutiny of Mr Farage and helped reveal his "nasty side" on issues including immigration, gay marriage and women's rights.
A source said: "I don't think a lot of those views were being as focused on previously as they are now. I think part of that is because of the debate."