我續領BNO已經將declaration form 已2月11用speed post 寄去英國,但忘記我原來有本特區護照已過左期,放左係柜桶底,我都唔記得左，但我申請時,只填左有bno,並沒有申報，及沒copy一份寄去,真的忘記左,現在真的很擔心,可以怎樣處理？

There is nothing you can practically do now.

In most instances, if your application is a straight BN(O) Passport renewal without any complications (such as name change, loss, etc.), the chance is the HM Passport Office will renew the passport without the copy of the HKSAR Passport.

Also if additional document is needed, the HM Passport Office will contact you by email per your application.

You should simply wait.