Companies and organizations that provide excellent customer service greet customers/patients with a smile and a greeting, listen to them, know their customer's preferences, and go above and beyond to make them happy. The interviewers ask this question to determine if your values align with the core values of the NHS, which are working together for the patient (customer), treating everyone with respect and dignity, committing to quality care, providing compassion, improving lives, and that everyone counts.
Think of how you like to be treated as a customer/patient. Then, think of how you provide excellent customer service, treating everyone how you want to be treated. Describe your actions to provide excellent customer service to all, showing the interviewers you will be an asset to their administrative team if hired. If you have received an award or recognition for your customer service, be sure to include that in your response.