If you have immigration permission that allows you to work, you do not need to get any further approval.
An employer must check that your work condition permits you to do the job for which you have applied. The Home Office calls this a right to work check. An employer must conduct this check in a way that does not discriminate against you.
An employer's guide to right to work checks
Code of practice on avoiding unlawful discrimination while preventing illegal working
You need to get a share code. Your share code is valid for 90 days and you can use it more than once during that period. The code must begin with 'W'.
View and prove your immigration status
You give this share code to your employer so that they can conduct an online check.
View a job applicant's right to work details
If you cannot get a share code, talk to your employer.
You might be waiting for a decision on your application. Or you might have exceptional assurance. In these situations, an employer can use the Employer checking service. They must wait for Home Office approval before you can start work.
Your employer will also need to see information about the term dates for your course. This information can be in any format. For example, dates from your sponsor's website, an email to you or a letter to the employer.
If you are doing a work placement, your sponsor must provide details in a letter to your employer.
Sometimes, employers must also conduct criminal record checks before you can start work.
Check someone's criminal record as an employer
Criminal records checks for overseas applicants