This situation clearly does raise suspicion, however, you shouldn’t jump to conclusions.
When the employee returns to work, ensure that you hold a return to work interview with them to understand fully what their ailment was. Whilst you cannot turn the clock back and avoid this particular situation, you can certainly take some action to ensure that employees are deterred from doing it again. Having to face you and explain the details of their ‘illness’ – and lie through their teeth – may seem too high a price to pay for the benefit of having a day off.
The reality of this situation is that the employee may have lied to you. It may be explicitly included in your employment documentation that falsely claiming sickness – particularly if this includes the payment of occupational sick pay – is considered to be an act of misconduct. Even if this is not specifically stated, there is an implied rule in every contract of employment that breaches to the trust and confidence that must exist between employer and employee can be acted upon by the employer if the actions of the employee compromise this.
In order to take action against the employee for this, you would have to have a reasonable belief that the employee was lying and had in fact taken the day off to be able to fulfil the plans in relation to which he had requested the holiday. You do not need absolute proof – the bar for taking action against and even dismissing an employee because of conduct is not set so high.
In order to take action against the employee, you would need to do some investigation – the return to work interview could make up part of that.
If you do find that the employee has breached your rules then appropriate action should be taken. For an employee with a short amount of service, it may be possible for their actions to result in their dismissal. However, this is not a likely course of action for an employee with 2 or more years’ service if this is the first breach of rules by this employee.