The UK Independence Party could hold the balance of power after the next general elections, the UKIP leader claimed Friday after the party won its first ever parliamentary seat.

Triumphant Nigel Farage warned the Conservatives and Labour, the two leading political parties in the UK, that his party “is after them.”

Farage’s remarks came after his anti-EU party won its first British parliament seat on Thursday by a huge majority.

UKIP’s Douglas Carswell took the Clacton seat in a byelection on Thursday, securing 12,000 more votes than his Tory rival.

Carswell had represented Clacton for the Conservatives, leaders in the current coalition government, until last month when he defected, triggering the byelection.

At a second byelection on Thursday in the Greater Manchester constituency of Heywood and Middleton, Labour narrowly held the seat despite a strong challenge from the UKIP contender.

The byelection, triggered by the death of Labour MP Jim Dobbin, saw Labour’s LizMcInnes take 41 percent of the votes, while UKIP’s John Bickley won 39 percent – up from 3 percent in the 2010 general election.

In a TV interview after the final results, Farage said that Thursday "was the biggest and best night in UKIP's history”.

He strongly criticised David Cameron, the prime minister and Conservative leader, and Labour leader Eid Miliband for “underestimating” his party.

"The whole of British politics has been shaken up in a way that the complacent Westminster class could never even have contemplated,” he added.

"Something big is happening here. People want change. They have had enough of career politicians in three parties who don't even understand the problems they face in their everyday lives. People want real change,” he said

"We've got a chance here in a general election next year that is likely to be very tight, in an election in which no one party is likely to have a majority - if UKIP can keep this momentum going, we could find ourselves next May in a position where we hold the balance of power."

The UKIP breakthrough came a few months after the party won 27.5 percent of British votes cast in the 2014 EU parliamentary elections.

Conservative Party Chairman Grant Shapp said the result in Clacton was a "wake-up call," warning that while UKIP were a threat to all the Westminster parties, they "cost Conservatives seats."

He believes this would put Miliband "one step closer to Downing Street."

Miliband commented: "there won't be a shred of complacency from us as we reach out to all those voters who didn't vote Labour and those who didn't vote at all."

A general election will be held on 7 May next year.