The UK Independence Party, for years led by its charismatic figurehead Nigel Farage, suffered a collapse in support at local elections held around England, Scotland, and Wales.
By lunchtime in Britain, UKIP had lost all the seats that it held, and failed to make any gains.
In the years leading to the referendum, UKIP wielded an influence far beyond its political representation. It never gained more than one MP in the UK parliament, but the former Conservative Prime Minister David Cameron was so worried about the prospect of losing support from voters skeptical of the European Union in the 2015 general election that he promised the in-out referendum.
Farage resigned as party leader in the wake of the subsequent 2016 referendum, declaring his work complete. Since then, UKIP has been riven by infighting and factionalism.
Early results indicate the governing Conservative Party has made significant gains at UKIP's expense. The Conservatives have adopted an increasingly hardline approach to Britain's exit from the European Union, undercutting UKIP on its central message and apparently wooing voters back to the mainstream.
UKIP leader Paul Nuttall said it had been "been a difficult night" for his party, adding, "We are the victims of our own success."
The main opposition Labour Party has suffered losses in areas where it has traditionally been strong, such as south Wales, according to early results from the Press Association news agency, while the Liberal Democrats have seen a patchy performance so far, failing to make the headway they hoped for in southwest England.
Thursday's elections for county council seats and mayoral posts are being closely scrutinized for clues to how the major parties will perform in the snap general election in five weeks' time
. Campaigning is now well under way, against the backdrop of increasingly contentious debate over Brexit
ahead of formal negotiations.
While the local election results are not yet complete, Prime Minister Theresa May is likely to be encouraged by her party's strong showing so far, which may suggest her gamble in calling the snap general election will pay off.
With results declared in 26 councils, UKIP had lost all 30 seats it held and failed to win a single contest. Its losses were centered in Lincolnshire, a former UKIP stronghold where Nuttall is standing for election on June 8, Hampshire and Essex, PA said.
Nuttall: 'Victims of our own success'
In a statement, Nuttall said his party's candidates had worked hard but there was "nothing they could have done in the face of a big national swing to the Tories," as the Conservatives are also known.
"Our electoral success over recent years was a key driver in forcing the Conservatives to embrace our cause under a new prime minister who was campaigning for a Remain vote in the referendum a year ago," he said.
"Mrs May's public dispute with the EU in recent days -- which led to her speaking about standing up to Brussels in an eve-of-poll statement in Downing Street -- was particularly fortuitously timed for the Conservatives."
UKIP enjoyed a surge of support at the 2015 general election under the leadership of Farage, one of the key players in the Brexit campaign, taking a 12.6% share of the vote. The party finished second in 118 of the 650 parliamentary contests but only gained one seat in the House of Commons because of the UK's first-past-the-post system.
Farage famously flew to New York to meet with Donald Trump shortly after his election
as US President, having campaigned with
him during the 2016 Presidential race. He was eventually replaced as UKIP leader by Nuttall
, a Member of the European Parliament.
Sunday Telegraph columnist Liam Halligan told CNN that while UKIP's success had effectively pushed former Prime Minister David Cameron into calling the referendum, it now struggled to seem relevant.
"Now because the Brexit process is happening, because Theresa May in the eyes of many people who voted leave is really going for it, she isn't going to hold back, there isn't going to be any watering down -- then UKIP's role as 'watchdog' of Brexit looks like a bit of an anachronism," he said. "They look a bit past their sell-by date, particularly because they have lost Farage."
National vote indicator?
UKIP's Roger Helmer, a European Parliament member, tweeted Friday that without his party, Brexit would never have happened.
"Without UKIP, we wouldn't have had a referendum; we wouldn't have won the referendum; and the Tory Party would never have backed Brexit," he said.
With full results declared by 20 of the 88 councils holding elections -- all of those in Scotland and Wales and 34 in England -- the Conservatives had control of nine authorities, five of them gains, PA reported. Labour meanwhile had control of two councils and had lost control of two in Wales.
Elections were also held for eight regional mayoral posts in England, six of them newly created.
Counting is expected to continue into Friday.
Online market research firmYouGov warned against reading too much into the results, saying that local elections have tended to be a poor indicator of national votes.