A co-pay is like excess on a UK car insurance policy. You'll need to contribute up to that co-pay value before your insurance kicks in. For example, you might need a prescription for medication and have a co-pay equivalent to around £5. In that case, you pay the £5 to the pharmacist along with your health cover details, and they claim back the balance from your provider. Alternatively, you may need to pay upfront and claim the costs back. Your refund will be for the value paid, less the co-pay.