If your visa is inside an expired passport it cannot be used to prove your right to work in accordance with the Home Office right to work checklist
I have unlimited leave to remain / indefinite leave to remain it doesn't matter if it has expired?
If you have unlimited leave to remain/ indefinite leave to remain, this cannot be demonstrated in an expired document. Your status needs to be renewed, by transferring your leave to a new Biometric Residence Permit or Card.
My visa has not expired, or does not display an expiry date, do I still need to provide a visa inside my current passport?
Yes, the validity of your visa only remains valid when it is placed inside a current passport which has not expired.
I have travelled with my visa inside an old passport so why cannot I use it for the right to work check?
The rights to enter, live and study in the UK may have different conditions to the rights to work in the UK. As such, only those documents on the Home Office right to work checklist can be used in the right to work check
What document can I provide instead?
You will need to transfer your visa to a UK Biometric Residence Permit.