UKIP gains five councillors at West Norfolk and King's Lynn Borough Council
Five independent councillors have joined the UK Independence Party in Norfolk.
The UKIP recruits are members of West Norfolk and King's Lynn Borough Council, where Conservatives still hold a large majority.
UKIP leader Nigel Farage said: "These individuals have realised the old parties have forsaken the interests of the British people."
Ashley Collins, elected in 2013, was the only UKIP member on the council.
The five who have joined UKIP are June Leamon, Stephanie Smeaton, Michael Pitcher, Michael Langwade and Paul Foster.
Four of the five, with the exception of Ms Leamon, were Conservative councillors before they became independents.
Explaining his decision, Mr Foster said: "The home secretary admitted the government were not going to hit their immigration targets.
"This year 260,000 migrants have come into the country requiring six and a half towns the size of King's Lynn to accommodate them.
"We do not think the hard working tax payers should be made to pay for infrastructure because of Conservative mistakes at national and local level."
Analysis by Political Correspondent Andrew Sinclair
When people defect to another party at local council level it is often a personality clash rather than an ideological difference behind the move. In many ways that seems to be what's happened here.
All five of the new UKIP recruits agree with their new party's stance on immigration and Europe, but they also talk about being unhappy over the number of homes being built in the borough and they complain about the Conservative Council leader Nick Daubney.
Mr Daubney in turn says the four councillors who used to be in his party often opposed his policies and were "quite bitter" at being passed over for promotion.
But it is still a coup for UKIP to gain five new councillors in one day. The party is saying that it is the largest single defection on any local authority and it follows hot on the heels of a defection in North Norfolk, another in Great Yarmouth and two on Tendring council in Essex.
And it is notable that rather than sit as an independent, which is what upset councillors usually do, these people are instead switching to UKIP.
They are not alone. In all, more than 70 local councillors across the country have moved to UKIP.
With less than five months to go until the general election this will give the party momentum and more foot soldiers on the ground. UKIP is predicting more will follow.
Nick Daubney, Conservative leader at the council, said: "We're not running scared, because they've been independent and I expected they would declare themselves for UKIP.
"The Conservatives need to be much clearer about our policies to control immigration and UKIP need to be more honest about what they stand for in overall council strategy."
Clive Joyce, borough councillor and chairman of the North West Norfolk Labour Party, said: "There's now a strong probability it will split the Conservative vote and cause considerable damage in next year's elections."
All of the borough's 62 seats will be contested on the same day as the general election in May.