A National Insurance (NI) number is a unique reference number used by the UK government to track your taxes and benefits. You need one before you can start any paid work in the UK — including part-time jobs.
Go to gov.uk and search "Apply for National Insurance number". The application is online and takes about 15 minutes. You will need your passport or BRP/eVisa details and your UK address.
Some applicants are asked to attend an in-person appointment at a Jobcentre Plus to verify their identity. Bring your passport and proof of address. Not everyone is asked for this.
Your NI number arrives in a letter within 4–8 weeks. It looks like: AB 12 34 56 C. Keep this letter — never share your NI number with anyone you do not trust.
Yes — you can start working before your NI number arrives. Tell your employer you have applied and give them the number once you receive it. You cannot legally work without having applied.
Student visas allow up to 20 hours of paid work per week during term time, and full time during holidays. Working more than this is a visa violation. See the Visa Compliance guide for details.