As the refusal letter of the context question states, the papers were decided to be a false representation because they are either
- used by an imposter [as in: he is not the person the papers claim to be]
- has been obtained fraudulently [as in: the information given to the issuing country were not correct]
The UK authorities reasoned, that your statements were wrong and that as a result the papers must either belong to somebody else or were obtained fraudulently. Possession of such ID papers (including passports) is a crime under Identity Documents Act 2010, s.6 b & c:
It is an offence for a person (“P”), without reasonable excuse, to have in P's possession or under P's control—
(b)an identity document that was improperly obtained,
(c)an identity document that relates to someone else,
and s7:
(1)For the purposes of sections 4 to 6 “identity document” means any document that is or purports to be—
(c)a passport issued by or on behalf of the authorities of a country or territory outside the United Kingdom or by or on behalf of an international organisation,
(d)a document that can be used (in some or all circumstances) instead of a passport,
As such, the possession of the papers under a fake name for a state that does not offer dual citizenship but not having repealed the one before makes the second papers improperly obtained or belonging to somebody else, which is a crime punishable with up to 2 years in the UK, as Section 7 C explicitly says "passport issued by a country outside of the UK"