Understanding your CoS reference number

Every genuine Certificate of Sponsorship issued by a UK employer carries a unique reference number generated through the UKVI Sponsor Management System (SMS). Understanding this number and how to verify it is a key part of protecting yourself from fraud.

The reference number format.

A genuine CoS reference number is eleven alphanumeric characters. It is generated automatically by UKVI systems when a licensed sponsor assigns a Certificate of Sponsorship to a named worker. The number cannot be created outside the SMS system.

What fraudsters get wrong.

Forged CoS documents often contain reference numbers that are: the wrong length, use incorrect character combinations, or replicate numbers from genuine documents issued to other workers. While the specific validation algorithm is not public, structural inconsistencies can be identified.

How to verify.

The reference number should be provided by your employer through formal channels — not via WhatsApp or personal email. If you have the reference, you can ask the employer to confirm it matches their SMS records. SponsorShield also performs reference format validation as part of the document verification process.