According to the JCQ, which has a set of rules drawn up by all the exam boards, of your exam is over an hour long, you can be up to an hour late and your work will be accepted, but an exam officer will still have to explain the situation do they know you were late and you didn't just get 57 minutes extra. Past an hour late for the exam, the exam board will reject the work unless you can prove you were in isolation for the period before it started. If you were 57 minutes late, unless told otherwise, you are completely fine.
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