Border guard was wrong. UK used passenger records from transport companies to determine when someone left the country, not face recognition.
They do however use face recognition when you take a domestic flight from an international terminal. Then they take a photo of you just before security and compare that when you board. To me this seems like an overly complex solution to a problem that would normally by solved by having a domestic section of the terminal, but I’m sure they had their reasons.
And this week it's lead to people's child benefits being stopped because they were deemed to have left the country and not returned, because their names were on passenger manifests: https://www.theguardian.com/society/2025/oct/31/woman-flight...
God, a well functioning democractic society, the UK is not...