CoS Letter UK: What It Is and What It Should Contain
A Certificate of Sponsorship, often called a CoS letter by employers and applicants, is one of the most important parts of the UK work visa process. Although people sometimes refer to it as a letter, it is not a physical document. It is a digital record created by a licensed sponsor that confirms a genuine job offer and provides all the information required for a work visa application. Without it, a Skilled Worker or Temporary Worker visa application cannot proceed.
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A CoS acts as the Home Office link between the employer and the worker. It confirms that the job meets the correct skill and salary rules and that the sponsor is taking responsibility for the worker throughout the visa period. Because of this, accuracy in every section is essential.
Key Takeaways
- The CoS is an electronic record, not a paper document.
- It proves that a valid job offer exists under UK immigration law.
- A defined CoS applies to Skilled Worker applicants who are applying from outside the UK, while an undefined CoS is used for workers who are already in the UK.
- Each certificate is valid for three months and must contain accurate details.
- Employers, not workers, must pay the CoS fee.
Understanding the CoS Letter
A CoS is an online record issued through the Sponsorship Management System, which is the portal used by all licensed employers. The worker never receives a physical copy. Instead, they receive the unique reference number and use it during their visa application. This number proves that the job is genuine and that the sponsor has confirmed all required details.
Every CoS has an eleven-digit reference number that starts with the letter C. This number is the key link between the employer’s sponsorship duties and the worker’s visa application.
Types of CoS
The UK immigration system uses two primary categories of Certificates of Sponsorship.
Defined CoS
This category applies to Skilled Worker applicants who are submitting their visa application from outside the UK. Employers must request a defined CoS through their SMS account, and approval typically takes one working day. In some cases, UKVI may carry out additional checks, which can extend the timeframe.
Undefined CoS
This type is used for Skilled Worker applicants who are already inside the UK and need to switch into the route or continue their current permission. It also covers most other sponsored categories, including Temporary Worker roles. When a business applies for a sponsor licence, it must give an estimate of how many undefined certificates it expects to issue during the first year.
What the CoS Letter Should Contain
Every CoS contains specific details about the sponsoring employer and the worker. Each entry must be correct, since any mistake can lead to a visa refusal or raise compliance concerns for the sponsor.
- Employer Details
- Worker’s Personal Details
- Job Information
- Salary and Hours
Basically, the CoS will contain all the information about the role, the employer, and the details about the employment contract.
How to Verify and Use a CoS Letter
Once the employer assigns a CoS through the SMS, the worker will receive the reference number and job details. The worker should then:
- Check that all personal and job details match their offer letter and passport exactly.
- Confirm that the sponsor’s licence is active by searching the Register of Licensed Sponsors on GOV.UK.
- Ensure the start and end dates listed on the CoS are correct and within the visa application window.
- Apply for the visa within three months of the CoS assignment date. Applying earlier or later can result in rejection.
Get to know: Check Sponsor Licence UK: How to Verify Company Sponsorship
Need Help From An Expert?
If you need support with Certificates of Sponsorship, sponsor licence management, or Skilled Worker visa compliance, Gulbenkian Andonian Solicitors is ready to guide you through each requirement with accuracy and care. Our business immigration team advises employers and workers across all sectors and helps resolve issues before they affect applications.
Contact us to receive clear, practical advice tailored to your situation and keep your sponsorship duties fully protected.
FAQs
A CoS cannot be reassigned to another worker once issued. If the worker does not use the certificate within its validity period, the employer must withdraw it through the Sponsorship Management System and then assign a new certificate to another eligible applicant. Each assignment requires a new fee and accurate details.
A worker can technically hold more than one CoS at once, but they can only use one for their visa application. They must ensure the chosen certificate reflects the correct job, salary, and sponsor before submitting their application to avoid delays or conflicting information.
Employers must retain all CoS documents and related evidence for the full duration of the worker’s employment plus an additional year. These records must be available for Home Office audits and include job details, recruitment documentation, salary evidence, and sponsorship correspondence.
A CoS is the certificate assigned to a worker. An A-rated licence is the status given to an employer by the Home Office. Only A-rated sponsors can assign CoS. If the licence is downgraded, the business may face limits on issuing certificates or additional compliance checks.
If a passport is renewed before the visa application is submitted, the employer must update the CoS with the new passport details. Incorrect or outdated passport information can cause issues during the visa process and may result in a refusal.
