The UK Independence Party (Ukip) was blaming an "internal error" today for keeping its party's name off ballot papers in London, potentially losing them the chance of representation on the capital's assembly.
After nomination papers were filled in incorrectly, the party's contender for mayor, Lawrence Webb, and candidates for the London Assembly were listed as "Fresh Choice for London", rather than Ukip.
Party leader Nigel Farage said the bizarre blunder probably meant large numbers of would-be supporters assumed Ukip was not taking part in the ballot and gave their vote to someone else.
The eurosceptic party had been polling at around 8% in the capital in the run-up to yesterday's vote - enough to secure third place in the mayoral race for Mr Webb and possibly two seats in the Assembly, where Ukip has been unrepresented since two members defected in 2005.
"We can only put our hands up and say sorry to voters who wanted to back us but couldn't find our name on the ballot paper," said Mr Farage.
"We hoped and expected to get two seats, but this has cost us dear. It is a lesson hard learned."
The mistake may have boosted Boris Johnson's showing in the first round of the mayoral poll but is unlikely to affect the final outcome, as most Ukip voters are thought likely to give their second-preference votes to the Conservative candidate.
Elsewhere in the country, Ukip performed well despite seeing only limited gains in council elections.
With counting complete in 177 out of 181 councils, the party had won nine seats - unchanged from their position at the start of voting.
But Mr Farage said they had seen their share of the vote rise across the country, but had been unable to translate this into seats on councils.
"Our share of the vote is going up and up and up, very steadily, very surely," he said.
"Yes, we are getting Conservatives voting for us but it is not just Conservatives because those results are the same in Labour seats as they are in Tory seats.
"We haven't quite got to the level where we are bursting through and winning seats in very large numbers. If we continue this momentum, then next year and the year after we will start to win council seats in real numbers."
He said that Ukip's appeal was not simply confined to European issues.
"We are talking about immigration, the fact that we still have a total open door to the whole of eastern Europe. We are talking about green taxes and the damage it is doing to British industry. We are talking about the need for selective education. There is a whole raft of policies here," he said.
"For the Tories to attempt to eat into our vote, it will mean Mr Cameron changing its entire manifesto."