If an individual makes an in time application to extend their permission to stay in the UK, they can remain in the UK under their previous visa conditions whilst their application is decided. This continues even if their original permission expires.
To confirm they have the right to work whilst the application is pending you would normally submit a request to the Home Office Employer Checking service and they respond within 5 working days.
Now, if the individual holds an eVisa, you can ask them to provide you with a share code and the Online Checking Service can be used. This will provide an instant online Right to Work check.
A Home Office document showing the application was submitted in time plus the Employer Checking Service PVN or Online Check will provide you with a Right to Work check for 6 months.
