Voters in Barnet were made to wait as ballot papers failed to turn up to some polling stations on time.
Five polling stations in the borough were without the required papers for up to 20 minutes after the elections began at 7am.
A spokesman for Barnet Council said a there was a problem last night with the automated system for allocating the borough's 175,000 ballot papers.
The allocation had missed 20 polling stations meaning the process had to be carried out manually by the electoral registration team.
The spokesman said the team worked tirelessly throughout the night to ensure all 160 polling stations opened on time, but he added: "Unfortunately, a handful of polling stations did not receive their ballot papers until some minutes after 7am and we sincerely apologise to those voters affected.
"Polling stations are now in possession of ballot papers and will remain open as normal until 10pm, so people who may have missed the vote earlier have the opportunity to go back."
The five polling stations affected were all in Mill Hill, and included Mill Hill East Station, Dollis Infants School, Barnet Impact, St Paul's Church Hall and Courtland JMI School, which was last to have its papers delivered at 7.21am.
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