A CoS belongs to one sponsor and one role
A Certificate of Sponsorship is not a portable document. It is issued by a specific sponsor for a specific role, and it cannot be transferred between employers. If a sponsored worker moves to a new employer, the new employer must assign a new CoS and the worker must make a new visa application before starting work. There is no exception to this, and no mechanism for a previous employer to "hand over" a CoS number.
The risk when a candidate says their CoS was transferred
If a candidate tells you their current or previous employer transferred a CoS from an earlier sponsor, treat this as a serious red flag. It means that at some point the worker changed employer without a new CoS and without a new visa application, and has therefore been working in breach of their conditions, even if a right to work check shows valid permission until a future date.
A right to work check confirms permission to be in the UK; it does not confirm the worker is complying with their sponsorship conditions. Sponsored workers may only work for the sponsor and in the role stated on their CoS, plus permitted supplementary employment.
What this means for you as the prospective sponsor
A breach in the worker's history does not automatically prevent you from sponsoring them, but it will need to be addressed transparently in both the CoS request and the visa application
Applications with unexplained employer changes and no corresponding CoS assignments routinely attract caseworker scrutiny, and concealing the history risks refusal
Obtain the worker's full sponsorship history in writing: each employer, dates, and the CoS reference for each move
Take case-specific immigration advice before assigning a CoS to a candidate with a gap or irregularity in their sponsorship history
Due diligence checklist before sponsoring an already-sponsored worker
Confirm the candidate's current sponsor and job title
Ask for evidence of a new CoS and visa grant for every employer change in their history
Complete a right to work check, but do not treat it as proof of compliance
If anything does not line up, pause and seek advice before assigning a CoS
Government guidance: https://www.gov.uk/skilled-worker-visa/change-job-or-employer