If I don't respond to Britannia's comments, would that lower my odds of winning the appeal?
That depends on whether they have rebutted all your points? If they haven't, point this out to the POPLA assessor in your response to the operators evidence.
Whatever the outcome, it is not binding on you although, I'm sure you'd accept a win.
It will all depend on which POPLA assessor makes the decision. If your appeal is unsuccessful, it has no bearing whatsoever on any future action.
My advice is to check the operators response and point out anything that has not been properly rebutted. If you lose, never mind. You still do not owe them any debt.
If they want to try and revere any alleged debt, they will have to make a claim in the county court and prove their case. You would easily defend any claim which is likely to be struck out anyway.
The only risk, which is minuscule, is if it actually went all the way to a hearing and you were unsuccessful would be ~£200 or less and no chance of a CCJ on your credit record. However, as I have stated and based on years of experience adding on these cases, the most likely outcome of a claim is that it will either be discontinued or struck-out.
With that in mind, you can make a decision on what to do should your POPLA appeal be unsuccessful.