More on this mixup from The Evening Lack of Standards.

“A spokesman for Brent council said: “The mistake was identified within the first hour of opening at which point electors were advised to return to the polling station later in the day when the correct ballot papers would be available.”

“The polling station was issued with correct ballots papers by 9am. About 50 people had already voted. They are being contacted to explain the problem and asked if they could return to vote later in the day. Every effort is being made to rectify the problem and we apologise for the inconvenience caused.”

[...] was a long and tense night with some low drama at the first validation following the ballot paper mixup in Willesden Green and the re-routing of the Hampstead and Kilburn ballot boxes via Camden. The ballot counters of [...]