Certificate of Sponsorship (CoS): A Guide for Employers and Workers

The Certificate of Sponsorship (CoS) is a fundamental document in the Skilled Worker visa process. Both employers assigning CoS and workers relying on them need to understand how they work. Our Bolton immigration solicitors explain.

What is a Certificate of Sponsorship?

A CoS is not a physical document — it is a unique reference number generated within the Sponsorship Management System (SMS) by a licensed sponsor. It contains key details about the sponsored job: role title, SOC code, salary, employer details, start date and duration.

Defined vs Undefined CoS

There are two types of CoS. A Defined CoS is used for workers applying from outside the UK for roles on the Shortage Occupation List or above the £38,700 threshold — these require prior UKVI approval. An Undefined CoS is used for most other applications, including in-country applications and switches — these do not require prior UKVI approval and can be assigned directly by the sponsor.

CoS Validity

A CoS is valid for 3 months from the date it is assigned. If the worker does not apply within this period, the CoS expires and a new one must be assigned. Workers must apply for their visa within 3 months of the CoS being assigned.

What Workers Should Check on Their CoS

Before relying on a CoS, the worker should verify that all details are correct — particularly the start date, salary and role details. Errors in the CoS can lead to visa refusal. If an error is identified, the employer must withdraw and reissue the CoS.

CoS Allocation

Sponsors have an annual allocation of Undefined CoS. If a sponsor runs out of allocation, they must apply for more via the SMS. The Home Office reviews requests and allocates additional CoS based on the sponsor’s business needs.