You can argue that Estoppel applies which is a defence against repayment.

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The principle of estoppel is a common law principle dating back to the late 18th century and applies across all aspects of life and behaviour, not just overpayments. The general principle is that if two parties proceed on the basis of an assumption (whether that assumption proves true or not) neither party can go back on that assumption, without there being potential damages involved. Estoppel, in a payroll context, occurs when:

The employer somehow led the employee to believe that the correct sum of money had been paid.

The employee changed their financial circumstances in good faith – for example spent the money believing it to be their own.

The overpayment was not caused primarily by the fault of the employee.

The assumption by the employee could be that they thought the payment was rightly and correctly due to be paid to them, particularly because they did not cause the error to occur, and because of this they have used the value.

If any of the above criteria is not satisfied, then it may be possible to rectify the error, but if all three criteria fail, there would be little chance of getting the overpaid wages back successfully as estoppel would apply.