COS UK: What Is a Certificate of Sponsorship and How Does It Work?

Despite the name, a Certificate of Sponsorship isn’t something you print or sign. It’s a digital record created by a licensed sponsor (usually the employer), uploaded via the Home Office’s Sponsorship Management System. It contains a unique reference number that ties together the job offer, the employer, and the worker applying for the visa.

If you’re hiring from overseas—or applying to work in the UK yourself—you’ll come across the Certificate of Sponsorship fairly quickly. It’s a standard part of the visa process, but there’s nothing standard about how crucial it is. Without a valid CoS, the application doesn’t move forward. It’s the anchor point for everything else.

Every little helps, hence, what’s inside matters: job title, salary, start date, working hours, sponsor licence number, and some basic information about the applicant. That data isn’t just there for formality—it’s how the Home Office checks whether the job meets the requirements of the specific visa route (usually Skilled Worker), and whether the employer is following the rules.

Once the CoS is assigned, the reference number gets passed to the applicant, who uses it as part of their online visa application. The visa can’t be submitted without it.

In the sections that follow, we’ll break down who can issue a CoS, how it’s used, common mistakes to avoid, and how it fits into wider compliance obligations.

What Is a Certificate of Sponsorship (CoS)?

A Certificate of Sponsorship (CoS) is a digital work authorisation record issued by a UK-licensed employer when they offer a job to someone who needs a visa to work in the UK. It’s not a document you download or print — it’s a unique reference number, created and stored in the Home Office’s system, that confirms the job offer and links it to the visa application.

The CoS includes key details like job title, salary, working hours, and start date, along with the sponsor’s licence number and the applicant’s personal information. It tells the Home Office:

• “This job meets the visa criteria,”
• “We, as the employer, are taking on legal sponsorship duties,”
• and “This person is genuinely being hired for this role.”

Without a CoS, a sponsored visa application (like the Skilled Worker visa) can’t be submitted.

Key facts:

• A CoS is required for most Skilled Worker and Global Business Mobility routes.
• It must be assigned before an individual can apply for a visa.
• Only organisations with a valid sponsor licence can issue a CoS.

Types of Certificates of Sponsorship

There are two types of CoS, each serving a different immigration route:

1. Defined CoS

Used for overseas applicants who are applying for a Skilled Worker visa from outside the UK.

• Must be requested by the sponsor via the Sponsor Management System (SMS).
• Allocated after approval by UKVI (UK Visas and Immigration).
• Valid for use in a visa application within 3 months of assignment.

2. Undefined CoS

Used for:

• Skilled Worker applicants already in the UK switching from another visa.
• Intra-company transfers, Graduate Visa switchers, or visa extensions.
• Sponsors receive an annual allocation of Undefined CoS.
• Can be assigned directly without prior UKVI approval.

Defined vs Undefined CoS — At a Glance

Important (!) Increasing Scrutiny on Defined CoS Requests

In recent months, there’s been a noticeable tightening in how the Home Office reviews Defined Certificate of Sponsorship (DCoS) requests. Several sponsors have reported being asked for additional documentation before a request is approved—something that wasn’t standard practice until recently.

Examples of requested documents include:

• Corporate bank statements
• Proof of how the migrant’s salary will be paid
• Employment contracts
• Organisational charts showing internal reporting lines

While most requests are still approved once the documents are submitted, this shift is adding pressure—particularly for smaller sponsors, who may not have these materials readily prepared or digitised.

It’s unclear whether this is part of a formal policy change or simply a pattern in caseworker discretion. Either way, sponsors should be prepared to justify the role and organisational structure with more than just job details and salary.

Who Can Issue a CoS?

A Certificate of Sponsorship can only be given by an employer or organisation that has a valid sponsorship licence. The Home Office checks out these sponsors and makes sure they meet strict rules, such as being able to keep an eye on and report on the workers they sponsor.

Sponsor obligations include:

• Ensuring that the job offer is genuine and meets salary and skill thresholds.
• Keeping accurate records of employment.
• Reporting changes in circumstances through the SMS (e.g., early termination, change of address).

Employers must also pay the Immigration Skills Charge, unless exempt, for each CoS assigned under the Skilled Worker route.

How to Check If Your Employer Can Sponsor You

Please note that before you apply for a job in the UK, you should check to see if the employer has a valid sponsorship licence. You can do this by looking at the official Home Office list of licensed sponsors.

Steps:

1. Visit the UKVI register of sponsors.
2. Use Ctrl+F to search by company name.
3. Confirm the sponsor has an “A-rating” and is approved for the relevant visa route (e.g., Skilled Worker).

Red flag: If a company claims they can sponsor but is not on this list, it may indicate misinformation or an unauthorised recruiter.

The CoS Assignment Process: Step-by-Step

Here’s how the process typically works for Skilled Worker visa applicants:

For the Employer:

1. Apply for a sponsor licence (if not already held).
2. Request a Defined CoS (for overseas hires) or use an Undefined CoS (for in-country).
3. Assign the CoS through the Sponsor Management System.
4. Provide the reference number to the worker.

For the Employee:

1. Use the CoS reference number when applying for a visa.
2. Submit supporting documents, including proof of qualifications and English language.
3. Attend a biometric appointment (if required).
4. Await a decision from UKVI.

Case Study: Assigning a CoS to an Overseas Worker

Example: TechHire Ltd

TechHire Ltd is a UK-based digital consultancy that recently obtained its sponsor licence. They want to recruit a full-time software engineer from Nigeria.

Here’s how they assigned the CoS:

• After conducting interviews, TechHire identified a qualified candidate with the required experience and English proficiency.
• The HR team submitted a Defined CoS request through the Sponsor Management System (SMS).
• Within 2 working days, UKVI approved the request.
• The CoS was then assigned to the candidate, including salary details and the job’s SOC code.
• The candidate used the CoS number to apply for a Skilled Worker visa and received a decision within 3 weeks.

This case highlights how the process functions in a real-world setting—and the importance of accuracy at each step.

What Information Does a CoS Contain?

Each Certificate of Sponsorship includes the following:

• Unique CoS reference number
• Job title and occupation code (from the Skilled Occupations List)
• Salary and working hours
• Start and end dates of employment
• Sponsor’s licence number
• Confirmation that the role meets immigration rules
• Indication of whether Immigration Skills Charge is paid
• Whether the job is on the Shortage Occupation List*

Please note, The Shortage Occupation List (SOL) in the UK has been recently replaced by the Immigration Salary List (ISL), which came into effect in 2025, includes updated salary thresholds and eligible roles. 

This information is reviewed by UKVI during the visa application process.

How Long Is a CoS Valid?

A CoS is valid for 3 months from the date of assignment. If the applicant does not apply for their visa within that period, the CoS expires and cannot be reused.

Once a visa is granted, the employment start date specified in the CoS becomes the reference point for the worker’s conditions of stay.

CoS and Visa Application Timeline – Sample Scenario

Timelines vary based on visa centre backlog, priority service, and country of application.

Costs Associated with a CoS

Immigration Skills Charge (ISC): What Employers Need to Know

In addition to the CoS fee, most employers must pay the Immigration Skills Charge (ISC) for each migrant worker they sponsor under the Skilled Worker route.

How to Know If You’re a Small or Charitable Sponsor

You’re likely a small sponsor if two or more of these apply:

• Annual turnover of £15 million or less
• Total assets of £7.5 million or less
• 50 employees or fewer

You’re a charitable sponsor if you’re:

• A registered charity in the UK, or
• An exempt/excepted charity, or
• An ecclesiastical charity set up for charitable purposes

Not on the register? You’ll need proof of charitable status from HMRC.

If you’re unsure, contact the Business Helpdesk:
businesshelpdesk@homeoffice.gov.uk

Exemptions apply if:

• The role is in a PhD-level occupation.
• The worker is switching from a Student visa and remains employed for under 6 months.
• You’re sponsoring a Graduate Trainee under the Global Business Mobility route.

Non-payment can lead to the rejection of the visa or penalties under sponsor compliance rules.

Shortage Occupation Roles and Salary Discount

If the role is on the Shortage Occupation List, the applicant can benefit from:

• Lower salary thresholds
• Reduced visa application fees

For example, a Skilled Worker applying for a shortage role only needs to meet 80% of the standard going rate.

The sponsor must still assign a CoS stating that the job falls within a shortage occupation and select the correct code from the list published by UKVI.

Assigned vs Unassigned CoS: What’s the Difference?

• Assigned CoS: Given to a named individual for a specific job. It can only be used by the person it was issued to.
• Unassigned CoS: Held in reserve by the sponsor. Not linked to any individual yet. Can be assigned later.

Employers managing high turnover or seasonal hiring often maintain a pool of unassigned CoS to streamline onboarding.

Common Mistakes Sponsors Make (and How to Avoid Them)

Even licensed sponsors occasionally make errors that can delay or jeopardise visa applications. Common pitfalls include:

1. Using the wrong SOC code
   Choosing a code that doesn’t match the actual job duties can lead to visa refusal. Always refer to the latest Skilled Occupation List and cross-check descriptions.
2. Assigning a CoS too early
   A CoS should only be issued after a genuine job offer has been made and the start date is confirmed.
3. Failing to meet the salary threshold
   Ensure the role pays at least the minimum salary as per visa rules, including any uplift for shortage roles or new entrants.
4. Not documenting recruitment
   For jobs not on the Shortage Occupation List, sponsors may need to demonstrate a fair recruitment process. Keep job ads, applications, and interview notes.
5. Missing sponsor duties
   Sponsors must report changes (e.g., job role, location, early termination) within 10 working days via SMS.

Can a Certificate of Sponsorship Be Withdrawn?

Yes. A CoS can be withdrawn by the sponsor before the visa application is made. Once the visa has been granted, the sponsor must notify UKVI if:

• The employee does not start work
• The role changes significantly
• The employment ends earlier than expected

UKVI may also revoke the sponsor’s licence if there are repeated breaches of immigration compliance.

Final Thoughts

The Certificate of Sponsorship (CoS) is the most important part of the UK work visa routes, especially for skilled workers. It’s not just a reference number; it’s a legal promise by the sponsor to hire the worker in accordance with immigration rules.

For employers, properly assigning and managing CoS is important for staying compliant and getting the best international talent. Getting a CoS is the first step for applicants on their visa journey.

Need Help Navigating the Sponsorship Process?

At Barar & Associates, we support UK businesses with:

• Securing and maintaining sponsor licences
• Assigning Certificates of Sponsorship correctly
• Ensuring full compliance with Home Office reporting duties

Whether you’re hiring overseas talent for the first time or managing an established sponsorship programme, we can guide you through the process without the jargon or guesswork.

Get in touch to speak with one of our immigration lawyers in confidence.

Frequently Asked Questions

Q1: Can I use one CoS for multiple visa applications?
No. A CoS is tied to a single individual and cannot be reused after a visa decision is made.

Q2: What happens if my visa is refused after being assigned a CoS?
The CoS cannot be reused, but the sponsor may assign a new one depending on the reason for refusal.

Q3: Can I switch employers using the same CoS?
No. Changing employers requires a new CoS and a fresh visa application under the new sponsor.

Q4: What if my employment start date changes?
Sponsors should update the CoS or notify UKVI through the SMS.

Q5: Is the CoS the same as a work permit?
Not quite. A CoS is one part of the process. A visa must still be granted based on the CoS to permit work in the UK.

Disclaimer: UK immigration rules, regulations and government fees are subject to change at short notice. Applicants should consult the latest Home Office guidance and official fee schedules—or seek qualified legal advice—before submitting an application.