ITV News Election Analyst Professor Colin Rallings has said Ukip's breakthrough is the "most significant trend in politics for 30 years."
He said: "I remember back in the early 1980s it was the Social Democratic Party, a break away group from Labour, did well in the elections and in the polls.
"They soon joined up with the Liberal Democrats so we became three parties again.
"But now we have a four party situation and in that respect Mr Farage is absolutely right. It makes thing very uncertain as to how the pattern of party loyalties will play out."
Read more: Labour in biggest danger of disappointment