Eurosceptic Conservative MPs said the results from across Europe proved their point.
Harwich and Essex MP Bernard Jenkin wrote on Twitter: "Some of us who opposed Maastricht 20 years ago predicted it would lead to the rise of the right in the EU: and here we are."
Douglas Carswell, the Clacton MP, said: "So maybe those of us who sometimes banged on about Europe were on to something?"
Foreign Secretary William Hague said Brussels had to acknowledge the "deep disillusionment and deep dissatisfaction" of voters across Europe.
He told the BBC he believed that Ukip's support would switch for next year's general election: "They can have a free hit , they can have a vote that does not have the consequence of bringing the wrong government in.
"So it is very different to a general election."
With Marine Le Pen's Front National set to top France's poll, Mr Hague said: "I think we should be concerned about some of these developments across the rest of Europe and that is why it is so important that the next European Commission, the European Council, the next European Parliament do get the message that there is rising discontent and tensions of many kinds in Europe."
Laura Sandys, the Conservative MP standing down in the South Thanet constituency where Nigel Farage is tipped as a possible contender at next year's General Election, told Sky News: "It is about being clear about what we want out of Europe.
"To be frank, I think most Conservatives actually understand the value of the (European) market ... but I also think we should not be defeated.
"We don't want to run for exits, we want to be part of big organisations and international organisations where our voice is heard."
Labour's deputy leader Harriet Harman said m any voters were set on punishing the main parties when they went to vote.
Acknowledging Ukip's victory, Ms 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."
Ms Harman said voters wanted to know the system was fair, that their wages were not being undercut by cheaper workers and that benefits were not being wrongly claimed.
Ukip leader Nigel Farage told the BBC: "We have sat there for 15 years in the European Parliament, with groups - the first five years I was there we sat with socialist parties.
"The thought Ukip would even contemplate sitting with the French National Front is something that was never going to happen and never is going to happen."
Mr Farage said his party's success would have a big impact on domestic politics.
He said: "We may well see one party leader forced out of his position as a result of tonight, we may see another party leader have to completely reconsider the idea they won't promise a referendum at the next general election and I suspect the Prime Minister will face calls from his own party for a much tougher negotiating stance."