If your VISA is in an expired passport, this is no longer a valid right to work document and needs to be replaced with a BRP.
You cannot use a valid visa in your expired passport to prove you have the right to work in the UK. You must replace your visa with a biometric residence permit (BRP).
Further information can be found on the UK Government website: https://www.gov.uk/transfer-visa/transfer-to-brp
To transfer your paper visa to a BRP, you can follow the information here: https://www.gov.uk/biometric-residence-permits/replace-visa-brp