Immigrationboards.com

My long and expensive immigration journey recently ended with naturalisation, and now I'm applying for a first passport.

I'm naturally distrustful of the "MUST" requirement to provide my other passport to the HMPO. Has anyone here any experience of not doing so? Obviously I've just spent many years supplying my other passport to the UK Border Force, so it's not as though I have anything to hide from them... I just don't like it.

You have to submit all uncancelled 'other' passports when you apply for a British passport.

If applying from abroad the application guide says there is no need to physically submit a foreign passport; copies of all pages may be accepted (with a proviso the original passport could still be asked for).

By signing the passport application form the applicant is agreeing (or at least asserts) that they have provided complete information and submitted all current passports, even if invalid/expired (etc).

According to the published rules a passport could, in the future, be withdrawn if it was found to be obtained by withholding material facts.

The only passports not required to be declared/submitted are cancelled ones or lost ones.
Even if lost the fact that it existed & has been lost has to be declared.

So the legitimate way to suppress existence of dual nationality & a second passport would seem to be:
cancel any other current passport just before applying in the UK.
Depending on the rules & policies of the dual country, that approach may not prevent reapplying for the dual passport at a future date.