Many thanks for your patience. First of all if you had not opted out of the 48 hour working limit, the employer should not have asked you to work more than that average. It is however an average, calculated over a 17-week rolling period. Therefore, it is possible to work some weeks more than that limit, as long as the average over 17 weeks is kept below 48 hours.
Assuming you still went over the average, there is no automatic right to be paid for that time. Your rights in this respect will relate to the right to be paid the National Minimum Wage at the very least. In effect, you Have to calculate the hours you did every month and the amount you were paid as a result. The average rate of pay must be at least equal to the NMW rate. If it fell below the NMW, that is when the employer will be in breach. However, if you received at least the NMW rate, they would not have to pay you anything extra on top of that, even if it meant you were working longer hours than legally required.
You may nevertheless negotiate with the employer to try and get compensated for that time and make it clear that you may have to report their breaches in relation to the working hours if they do not act fairly.
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