I'm afraid that standing on principles almost always involves a bit of risk.
I hadn't noticed the case that you have referred to – and our site team member @Andyorch has already commented on it that there is a lottery in so far as judges are concerned.
I haven't seen the claim form and I don't know precisely how it was argued in court. I feel very strongly that the decision is wrong because it effectively allows contractual terms to overcome statutory rights – and this has to be in error.
Whatever the case, it is most likely that Hermes will simply put their hands up and pay you out and if you had claimed 5 pounds more they would have done the same. Even if they had gone to court, your chances of winning on a claim for the £25 would be better than 95% and the worst you might have expected would have been for the court to refuse to award you the extra 4 pounds and simply to give you the £25.
I think that Hermes and the other courier companies rely on the fact that their customers don't have sufficient confidence to refuse to pay for the extra insurance.
Clearly this is something which needs to be tested at a reasonably within the court structure but of course this is most unlikely to happen given the value of claims.
I was sorry to see that your original reason for not claiming the full value was that
I asked you to post up your claim form. I think it will be helpful if you did that.
Bear with us while we discuss this behind the scenes - we want you to win just as much as you do but we want to find the right balance between maximising your claim without risking too much in court fees, and in possible court costs awarded to the defendant bank.