A Certificate of Sponsorship (CoS) is a reference number, not a physical certificate. The sponsor issues it through the Sponsor Management System (SMS). The applicant uses the number in their visa application.
What a CoS contains
Each CoS records the sponsored worker’s personal details, job title, SOC code, salary (including any allowances), start and end date, work address and a short description of duties. The SOC code matters most — it is the handle for checking the occupation against the eligible list and the going rate.
Any subsequent change to job title, duties, pay or location must be reported through SMS. Material changes may require the CoS to be reassigned or the visa to be extended.
Defined vs Undefined
Under the Skilled Worker route there are two categories:
- Defined CoS — for applicants outside the UK. The sponsor requests each one individually, citing the job details.
- Undefined CoS — for applicants in the UK (switching or extending). These come from the sponsor’s annual allocation.
A sponsor licence comes with an annual allocation of Undefined CoS; Defined CoS are requested as needed.
Validity window
Once assigned, a CoS is valid for use in a visa application for three months. Applicants who hesitate past that window must ask the sponsor to issue a fresh one.
Where to look next
If you are researching a potential sponsor, their entry in the directory shows whether they are A-rated (and therefore able to issue CoS without restriction). If they are B-rated, they cannot issue new CoS until they return to A.
Nothing above is legal advice. An immigration adviser can confirm what a specific employer can and cannot offer for your situation.
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