That’s fine, I suggest you stick to the position for now of saying you won’t comply with any resolution re removal of the stairs for now, and that you won’t sign any by-law.
More generally:
– stairs are not ladders and ladders are not stairs. They are two very different things. So for example if development consent were given for a ladder, that is not development consent for stairs.
– from the information you have given, it seems that the Council has never given approval for stairs. The statement on the Council file saying building work has been completed satisfactorily is not relevant to the stairs. The only document that you can rely on in relation to approval is approved plans, and any modifications and subsequent development approvals.
– the fact that you were sold the villa without a certificate is also irrelevant. When someone buys a property they should make their own enquiries, which would include inspection of council records, to ensure that what they are buying is ok, i.e. has Council approval etc.
As for the role of the OC – they are not a planning authority. It is not up to them to determine whether something is legal or not – only Council can do that. They can pass any resolution they like, but they can’t say whether something is legal or not. Ultimately that decision rests with the relevant authority which is the Council. Note that you could apply for approval from the Council now, although they may require alterations to bring what you have within scope of requirements.
You are right that the OC can make your life difficult, but there is another aspect to this – if the stairs are illegal, then the OC may be liable for any damage or injury that results from something going wrong, taking into account that they are aware there is an issue. As an owner you are also liable, and bear in mind that insurance may not cover the OC in circumstances where they are on notice of an issue and do nothing about it.