Nigel Farage sent a warning to Westminster as Ukip posted big gains at the local elections, telling David Cameron and Ed Miliband: "The Ukip fox is in the Westminster hen house."
Farage spoke after seeing his anti-EU party near the 100 council seat mark and become the official opposition in Rotherham, Yorkshire.
With results still being counted at time of publication, it looked like Ukip had turned Town Hall politics in to a four horse race - with the Liberal Democrats haemorrhaging seats.
Farage has vowed previously that Ukip will win seats at next year's General Election, or he will resign as party leader.
Farage said: "The Ukip fox is in the Westminster hen house. There are areas of the country where now we have got an imprint in local government. Under the first-past-the-post system we are serious players.
"There were two conversations going on last night. One was in Westminster amongst commentariat and MPs The other conversation was going on in Swindon where the Labour leader said we've been hurt by Ukip.
"Another conversation was going in Rotherham where Ukip won 10 seats and Labour won 11 seats. In the West Midlands Labour were saying Ukip were splitting our vote and letting the Tories in. This idea that the Labour vote just hursts the Tories is going to be blown away."
Ukip performed strongly in Essex as the Conservatives lost four councils in the county, as of Friday morning.
David Cameron got a slap in the face as Labour took control of Hammersmith and Fulham - reputedly one of the prime minister's cherished areas.
But Ed Miliband's party posted only moderate gains, overall. Concerns were raised about the party's performance, only one year out from a General Election. Labour MP Graham Stringer said the party had run an "unforgivably unprofessional campaign.
Labour MP and election strategist Douglas Alexander risked accusations of complacency in the face of the rise of Ukip, by insisting Labour was well placed to defeat Nigel Farage's army of angry old men.
He said: "If you look at the key battleground seats that are going to decide the outcome of that election, the dynamic of Ukip is playing itself out in a way that suggests actually Labour is well placed to win a whole number of those key seats."