Passports Required from 28 September for Ferry Travel Republic of Ireland to Great Britain

[Flying Snail]

In other words, if the OP has not omitted any other relevant information, the ferry companies decided to interpret "a document that confirms your identity and nationality." as "passport", which is clearly nonsense.

Easily fixed. Try to board a ferry without a passport, then take them to court. This is a civil matter, nothing to do with the government.

Take them to court for what? The ferry company are entitled to require customers to present passports if they want, they have given notice of this change in terms and if you turn up and are refused because you have not met their terms then you have no valid claim.