You must have a National Insurance number to work in the UK. It records your national insurance contributions and tax.
You need this as part of the right to work check. This takes place before you start any campus or part-time job.
When applying, you will need your passport or biometric residence permit. You can still apply if you do not have these documents but you may need to attend an appointment to prove your identity.
To apply for a National Insurance Number, visit the government website.