What document is required for a non-UK national to work in the UK?

Okay, let's break down why you need a National Insurance number to work in the UK. Think of it as your personal account number within the UK's social security and tax system. It's absolutely essential for anyone who wants to work and pay taxes legally. The National Insurance system was introduced in 1911 to fund social welfare programs. Today, it's how the government tracks your contributions to things like state pensions and unemployment benefits. When you start a job, your employer needs your National Insurance number to deduct the correct amount of tax and National Insurance contributions from your wages. Without it, you might face delays in getting paid or even have difficulty proving your right to work. While a driving license proves you can drive and a birth certificate confirms your identity and place of birth, neither of these documents directly relates to your eligibility to work and pay taxes within the UK system. So, while those other documents are important for other things, the National Insurance number is the key to employment.