The grandparent is slightly wrong. You are allowed to work 10 hours if your average over the next 6 months or 24 weeks does not exceed 8 hours a day. (Where "day" includes Saturdays but excludes Sundays and holidays)
There are a number of exceptions for extraordinary situations, that could not have been anticipated by the employer, to allow exceeding the 10 hours. However the rule about the average in the next 6 months or 24 weeks still applies.
There are a number of exceptions for extraordinary situations, that could not have been anticipated by the employer, to allow exceeding the 10 hours. However the rule about the average in the next 6 months or 24 weeks still applies.