Sending non British passport to passport office- why?

[MarmiteCoriander]

Sorry if this has been asked already. I live in England. I've applied for a British passport renewal online, but also have a valid passport from another country (I'm dual national). The confirmation email says:
Send the following:

• old passport


• any current or expired passports from other countries that haven’t been cancelled

Why do I need to send my other, valid passport and will they return it? It says my expired passport will be sent back, but nothing about my overseas one.

I've seen passport forums linked on MN, but cannot find any now. Any advice appreciated.

Anyone?

Further identification purposes and to confirm your eligibility for a British passport. Here's the copied answer to this question from when it was asked in parliament- the answer is from the Home Office.

"Where a dual national holds a passport issued by another country, HM Passport Office requires this to be provided in support of a British passport application as part of its range of checks to confirm the applicant’s identity and eligibility. This includes ensuring the British passport is issued in the same identity the holder uses for all official purposes.

We ask customers to send their original document to allow physical checks ensure it is genuine, and we can return it during the application process if requested. In countries where legal restrictions prevent a customer submitting their passport as part of their application, a ‘local service’ is in place to submit the application so officials can check the original document and send a copy to HM Passport Office in the UK."

I know it’s incredibly frustrating. Every time I have to send DDs’ other passports in I worry that I won’t get them back. This time it took 10 weeks for it to be returned. Completely unnecessary if you ask me.

@SapereAude I couldn't find anything on the passport renewal site at all, so thank you.

@Schulte Its just a worry that without ANY passport, I wouldn't be able to travel to my home country if something happened.
It my 1st time renewing my UK passport, and had no idea my other one would be taken for months also!

I feel your pain, I just renewed my daughter's UK passport. They were pretty good and sent her new UK one after 3 weeks but I'm still waiting for her valid other nationality passport to be returned. It's only been a week but it's still making me super anxious.

I tried to pay for a fast track appointment to renew so I could avoid sending it away but none were available.

I'm already worrying about doing mine as, like you, I am concerned about not being able to reach elderly family with my other passport, which is required to get in.

Good luck.

@orangina01 - Exactly the same as you. My mother is mid 70's and nan is 101! When I realised my British passport was 3 days expired, I thought 'well at least I have my other passport to travel if needs be'. I also tried to make a fast track appointment and non available. Off to the post office tomorrow to send them off though.