Defending a small claim online

[Levie]

A customer has issued a small claim against my business. It’s for faulty goods sold well over 6 years ago.
My defence is that the claim should be struck out as it’s over 6 years. Also, I’ve issued a credit to the original full purchase value which the customer has acknowledged, and I’ve offered to settle this in cash. (I can’t refund him without having his bank details. ) The claimant is v litigious and I think he will want to proceed with the claim if he can.

I have further strong arguments as to why the claim is unreasonable. Do I need to set these out now in my initial defence? Or do I leave this until or unless the claimant proceeds with the claim? Advice would be welcomed as I don’t want lose the opportunity to state my full case at a later stage.