Sending back passports question

[BrieAndChilli]

I have just renewed my kids passports online and need to send back the old ones. Can I send all 3 back in the same envelope or do they need to be sent separately? I cant see that it would make any difference but dont want to delay them!

I sent mine in separate envelopes because you have to put the application number on the envelope. Plus we had two different addresses to send to out of four applications.

The address has your reference number in it. So seperate envelopes.