Some Hong Kong friends asked me this today and I have no clue.
Hypothecate you're Hong Konger. You've hung on to your just 1 BN(O) passport, now expired, that you never renewed. Now you want to renew it, and the UK government (call it UK GOV) asks you to mail in that old expired passport. Before you mail it, you take pictures and make photocopies of the Holder's page.
But UK GOV loses your only BN(O) passport.
Does UK GOV even keep a record of all BN(O) passport holders? Can UK GOV just check its records, locate yours, and smoothly issue you a new BN(O)?
Or can UK GOV argue they can't issue you a new BN(O), because now you have no physical BN(O) passport even if it's their fault, and they can't verify you as BN(O)?