The Liberal Democrats were the night’s biggest losers as Nick Clegg paid the price for his gamble to position the party as the natural opponents to Ukip’s Euroscepticism.
In a humiliating set of results, the party lost all but one of the 11 MEPs it went into the contest with and was relegated to fifth place behind the Greens.
In Wales the Lib Dems lost their deposit and finished in sixth position.
The mauling led to fresh criticism of Mr Clegg’s leadership, but senior figures rallied around him despite the losses suffered in both the European and local elections.
Labour secured second place in the national contest with a strong performance in London, but the inability to deliver a win in a national poll or break through in key battlegrounds just 12 months before Ed Miliband hopes to enter 10 Downing Street will worry some in the party.
After 10 of Great Britain’s 11 regional constituencies had declared their results, Ukip had 23 MEPs and a 29.07% share of the vote - up 11.685 on 2009.
Labour had 18 MEPs and a 25.35% vote share, the Tories had 18 MEPs and a 24.56% vote share, the Greens three MEPs and a 7.85% share while the Lib Dems managed a solitary MEP and 6.85% of the vote.
The final result in Scotland will be announced later, but with only the Western Isles left to declare it appears the SNP and Labour will retain their two Scottish MEPs, with the Scottish Tories also keeping their European representative.
But the Liberal Democrats appear to have lost their one MEP, with that seat going to Mr Farage’s party, giving them a first foothold in Scotland.
Ukip’s opponents will scrutinise the stunning performance of Mr Farage’s “people’s army” for signs that the results are skewed by protest votes which may change at next year’s general election.
But in his acceptance speech after topping the poll in the South East, Mr Farage promised: “You have not heard the last of us.”
He said the victory was “just about the most extraordinary result that has been seen in British politics for 100 years”.
Mr Farage said the party “bit very hard” into the Labour vote in the North, almost topped the poll in Wales, gained a seat in Scotland and “we are genuinely a UK Independence Party”.
He told reporters: “The message is people have had enough of not being told the truth and not being given the opportunity to express their opinion.
“Five years ago the Conservatives won, giving us a cast-iron guarantee of a referendum they didn’t deliver.
“We have had the Liberal Democrats and Labour over the years making these promises and there’s a very strong desire in this country to have a different relationship with Europe.”
He said successive encouraging results in local elections gave Ukip a good grounding to win seats in Parliament.
He said: “We have proved in county council elections last year, district council elections this year, that we can win in the first past the post. Perhaps the most significant thing for us in the course of the last few days is we have built up clusters of local council seats and areas and that’s the model the Liberal Democrats used in the 1990s to build up in Parliament.”
Lib Dem party president Tim Farron, seen as a possible successor to Mr Clegg, said the Deputy Prime Minister should not face a leadership challenge despite the “staggeringly disappointing” European election result.
The Lib Dems had “paid the price” for the decision to fight a strongly pro-European campaign, he said, but he told Sky News that Mr Clegg should be praised for having the backbone to take an unpopular position over the EU and confront Ukip’s “threat to British cultural values”.
But Martin Tod, a councillor and member of the party’s federal executive, was scathing about the Lib Dems’ chances while Mr Clegg remained at the helm.
He told the BBC that voters would not back Mr Clegg: “What seems to be clear coming out of this is that they are not prepared to listen to our leader and that’s a really serious problem.
“It’s a problem that I think we need to address.
“You can’t lose all of your MEPs bar one and pretend that nothing has happened, that your strategy is perfect and you just need to carry on as you are and carry on delivering the leaflets and saying what we said in our leaflets this year and everything will be fine.”
The Tory leadership faced further calls for an electoral pact with Ukip to avoid a split in the right of British politics next year.
Daniel Hannan, who was returned as a Tory MEP in the South East region, became the latest elected Conservative to call for a deal with Mr Farage.
“For a party that is in government in Westminster, not to be being pummelled at this stage is pretty good news,” he told Sky News.
“It would be very sad if the two right-of-centre Eurosceptic parties at the general election were not able to find some way, at least in marginal seats, of reaching an accommodation so that anti-referendum candidates don’t get in with a minority of votes.”
Conservative Party chairman Grant Shapps has repeatedly ruled out any formal pact or local deals with Ukip.
In an indication that Labour believed there was a strong protest vote for Ukip, deputy leader Harriet Harman told LBC: “People have said they are voting Ukip even if they are a Labour supporter in order to give us a shake-up.”
Ukip was not the only Eurosceptic party to prosper in the elections, with a series of results across the continent underlining voters’ disillusionment with the political establishment.
One of the most significant winners was France’s far-right Front National party, which was the country’s outright winner with 26% support, some 4.1 million votes.
British National Party leader Nick Griffin been ousted as an MEP - but said Ukip supporters were racists who would turn back to his party when they realised Nigel Farage would not “send them all home”.
Mr Griffin was abandoned by voters in the North West four years after the BNP won two seats in the European Parliament - which was swiftly followed by a period of turmoil within the party.
After six months on taxpayer-funded severance pay, he said he intended to campaign in the region - partly by setting up food banks exclusively for “our people”.
Andrew Brons, who was elected for the BNP in Yorkshire and the Humber in 2009 but quit the party two years later, also lost his seat.