Some South Hampstead voters lost out at the by-election because they did not have photo ID.
It is the first time that voters in Camden have had to show photo ID to cast their vote after new rules came in this spring.
The four parties contesting the South Hampstead seat in the council by-election included information about the changes in election literature and campaigners for all the parties said they also told people about it on the doorstep.
However Kentish Town North councillor James Slater said he encountered voters who said they would miss out.
He said despite all the parties sharing information with voters “I think it’s a communication problem.”
Other voters thought the change was unjust, he said.
The by-election turnout was 30.22 per cent, down from 36.7 per cent in last May’s election, when voters returned three Labour councillors. However the low turnout is considered normal for a by-election.
Acceptable ID includes driving licences with photos, passports and bus passes.
Campaigners said not everyone can afford a passport or have a driving licence because they cannot afford a vehicle, or are eligible for a bus pass.
Tommy Gale, who was elected as the new South Hampstead Labour councillor, was out campaigning all day.
He said: “There been a few people saying they were turned away without ID.
“Someone had come back from work specially to vote and was upset about it,” he said.
Camden council’s election team is looking to see if voter ID was a problem.
The by-election comes ahead of next year’s London mayoral election in May and the general election.
The Electoral Commission is collecting data about the number of people turned away at the council elections outside London in May.
According to data compiled by the BBC, 26,165 voters in elections at 160 councils were initially turned away and 9,577 did not return with the correct ID.