Defined vs Undefined CoS

This article explains the rules around Certificates of Sponsorship (CoS) under the UK’s Skilled Worker visa route.

What this article is about:
Employers in the UK must hold a sponsor licence to employ most non-UK workers. One of the central duties of a sponsor is issuing Certificates of Sponsorship to eligible workers. There are two main types of CoS: defined and undefined. This article examines the legal and practical differences between these types, when each should be used, and the processes employers must follow. It also looks at the compliance responsibilities attached to CoS allocation and assignment, so that sponsors can avoid common errors and maintain their Home Office approval.

Section A: What is a Certificate of Sponsorship?

A Certificate of Sponsorship (CoS) is a digital document issued by an employer licensed by the Home Office to sponsor migrant workers under certain visa routes. It is not a physical certificate but an electronic record generated through the Sponsor Management System (SMS), which the Home Office uses to track compliance and control access to the UK labour market.

The CoS provides confirmation from the employer that they intend to employ the individual in an eligible role and that they meet the requirements of the immigration route being applied for, most commonly the Skilled Worker visa. The certificate contains specific details, such as the job title, occupation code, salary, start and end dates of employment, and the sponsor’s licence number. These details are crucial as the applicant’s visa application will be assessed against them.

A valid CoS is mandatory for a Skilled Worker visa application. Without one, an individual cannot apply under this route. The CoS acts as a bridge between the employer’s sponsorship responsibilities and the worker’s immigration permission, ensuring that the job offer meets immigration rules and that the employer is accountable for the sponsored worker.

Only organisations with a sponsor licence can assign CoS. This means the Home Office has already approved the employer as a suitable sponsor, subject to ongoing compliance duties such as record-keeping, reporting changes through the SMS, and preventing abuse of the immigration system.

By assigning a CoS, the employer is confirming to the Home Office that they have carried out the necessary checks, that the role is genuine, and that it meets minimum salary and skill thresholds. Misuse of CoS, or assigning one incorrectly, can lead to compliance action including downgrading, suspension, or revocation of the sponsor licence.

Section Summary
A Certificate of Sponsorship is a mandatory digital document linking an employer’s sponsorship licence to a worker’s visa application. It confirms the details of the employment and underpins compliance with UK immigration law. Only licensed sponsors can issue CoS, and their correct use is vital to maintaining sponsor status.

Section B: Defined Certificate of Sponsorship

A defined Certificate of Sponsorship (CoS) is required where an applicant is applying for a Skilled Worker visa from outside the UK. This type of certificate is not part of the employer’s annual allocation. Instead, it must be requested individually each time there is a need to sponsor a migrant for a role based in the UK.

The process begins with the sponsor submitting a defined CoS request through the Sponsor Management System (SMS). The request must include the details of the role on offer, including the occupation code, job title, proposed salary, and work location. The Home Office assesses whether the request meets the Skilled Worker eligibility criteria before granting approval.

In most cases, defined CoS requests are decided quickly, usually within one working day. However, the Home Office may take longer if further checks are required, for example where the role or salary level raises concerns about whether the job meets the immigration rules, or if the sponsor is newly licensed.

Once approved, the sponsor can assign the defined CoS to the worker, who can then use it to support their Skilled Worker visa application from abroad. A defined CoS has a limited validity period. It must be assigned to a worker within three months of being granted. Once assigned, the worker has three months to use it to apply for their visa. If the certificate expires, a new request must be submitted.

The defined CoS system allows the Home Office to scrutinise each overseas Skilled Worker application in advance, ensuring tighter control over immigration from abroad. For employers, this means they must be prepared to provide detailed information about the role upfront and ensure that the job meets all Skilled Worker route requirements.

Section Summary
A defined CoS is used for Skilled Worker visa applicants applying from outside the UK. Sponsors must request it individually through the SMS, and the Home Office will review the request before approval. Once granted, it must be assigned within three months, and the worker must apply for their visa within a further three months.

Section C: Undefined Certificate of Sponsorship

An undefined Certificate of Sponsorship (CoS) is required where a Skilled Worker visa applicant is applying from inside the UK. This includes individuals who are switching immigration categories, extending their leave, or applying for further permission to remain under the Skilled Worker route. Undefined CoS are also used for other sponsored work routes, such as Senior or Specialist Worker visas under the Global Business Mobility category.

Unlike defined CoS, which are requested case by case, undefined CoS are allocated annually to each sponsor licence holder. Employers must estimate their business needs in advance and request an allocation of undefined CoS when applying for or renewing their sponsor licence, or during the annual allocation renewal process. The Home Office reviews these requests and grants an allocation based on the sponsor’s past usage, compliance record, and projected recruitment needs.

Once approved, the allocation is made available to the sponsor via the Sponsor Management System (SMS). The sponsor can then assign undefined CoS to eligible workers within the limits of their allocation. If an employer underestimates their needs, they can submit a request for an increase to their allocation at any time during the year. The Home Office will consider the justification provided and may grant additional undefined CoS if satisfied.

As with defined CoS, an undefined CoS must be assigned correctly and within the rules of the relevant visa route. The details included in the certificate, such as job title, occupation code, salary, and work location, must be accurate and consistent with the role. Misuse or mismanagement of undefined CoS, such as assigning one to an ineligible worker, can result in compliance action against the sponsor.

Undefined CoS provide greater flexibility to sponsors by allowing them to assign certificates to workers without needing Home Office approval on each individual request. However, this flexibility comes with increased responsibility for sponsors to manage their allocation carefully and in compliance with the immigration rules.

Section Summary
An undefined CoS is used for Skilled Worker applications made from within the UK and for other sponsored routes. Sponsors receive an annual allocation, which they must manage and assign correctly. While undefined CoS give employers flexibility, they also carry significant compliance responsibilities.

Section D: Key Differences Between Defined and Undefined CoS

The distinction between defined and undefined Certificates of Sponsorship (CoS) is central to sponsor licence management. Both serve the same ultimate purpose—supporting a Skilled Worker visa application—but they differ in their application, process, and management.

The most important difference lies in where the visa applicant is applying from. A defined CoS must be used if the Skilled Worker is applying from outside the UK. An undefined CoS must be used if the Skilled Worker is applying from inside the UK, for example when switching routes or extending leave. Attempting to use the wrong type of certificate can invalidate the visa application and may trigger Home Office scrutiny of the sponsor’s compliance processes.

Another key distinction is the way each certificate is issued. Defined CoS are requested individually through the Sponsor Management System (SMS). The Home Office reviews the request and grants approval before the employer can assign it. This allows the Home Office to check the job against immigration requirements on a case-by-case basis for overseas recruitment. By contrast, undefined CoS are issued as part of an annual allocation. Sponsors must forecast their recruitment needs and manage their allocation throughout the year, only requesting top-ups if their allocation proves insufficient.

Defined CoS therefore give the Home Office greater oversight of applications made from abroad, while undefined CoS place greater responsibility on employers to use their allocation correctly. For sponsors, this means different planning considerations: they must ensure that their internal HR systems distinguish between defined and undefined CoS and that staff responsible for immigration compliance understand when each applies.

From a compliance perspective, the consequences of misuse are the same for both types. Sponsors risk licence downgrading, suspension, or revocation if CoS are assigned incorrectly or if the details provided do not meet the visa route requirements. Employers should therefore maintain robust internal processes for managing both defined requests and undefined allocations.

Section Summary
Defined CoS apply to Skilled Worker applications from outside the UK and require case-by-case Home Office approval, while undefined CoS apply to applications from inside the UK and are managed as part of a sponsor’s annual allocation. Both must be used correctly to avoid compliance action, making clear internal processes essential for licensed employers.

FAQs

What is the difference between defined and undefined CoS?

A defined Certificate of Sponsorship is required when sponsoring a Skilled Worker visa applicant from outside the UK. An undefined Certificate of Sponsorship is required for Skilled Worker applications made from inside the UK, such as extensions or switches, and for some other sponsored routes.

Do employers need both types of CoS?

Yes, most sponsors will need access to both. Employers who recruit Skilled Workers from overseas must request defined CoS as needed, while they also require an allocation of undefined CoS to cover workers applying from within the UK or other sponsored visa categories.

How long does it take to get a defined CoS approved?

Most defined CoS requests are decided within one working day, although the Home Office may take longer if additional checks are needed, particularly for complex roles, sensitive sectors, or newly licensed sponsors.

Can an undefined CoS be used for an overseas applicant?

No. An undefined CoS cannot be used to support a Skilled Worker application made from outside the UK. Attempting to do so will lead to a visa refusal and potential compliance issues for the sponsor.

What happens if an employer runs out of undefined CoS allocations?

Employers can submit a request for an increase in their undefined CoS allocation through the Sponsor Management System at any time. The Home Office will assess the request and may grant additional certificates if justified.

Conclusion

Certificates of Sponsorship are a core feature of the Skilled Worker visa route and the wider sponsorship system. Understanding the difference between defined and undefined CoS is essential for employers with a sponsor licence, as using the wrong type can lead to visa refusals and compliance action.

Defined CoS apply to Skilled Worker applicants outside the UK and require individual Home Office approval. Undefined CoS apply to applicants already in the UK and are managed through an annual allocation that must be carefully monitored by the sponsor. Both types carry strict rules on assignment, accuracy, and use.

For employers, the ability to manage CoS correctly is not just an administrative task but a legal duty tied to the conditions of their sponsor licence. Failure to comply can jeopardise their ability to sponsor workers at all. The Home Office actively monitors CoS allocation and use, including through compliance visits, meaning sponsors should expect scrutiny of their processes. With correct planning, strong internal systems, and a clear understanding of when each type of CoS is required, sponsors can minimise risk, streamline recruitment, and maintain compliance with Home Office requirements.

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